Light detecting element

ABSTRACT

This light detecting element has a simple configuration, and is highly sensitive to a prescribed wavelength region. The light detecting element comprises a positive electrode, a negative electrode, and an active layer that is provided between the positive electrode and the negative electrode, and that includes a p-type semiconductor material and n-type semiconductor material. The thickness of the active layer is at least 800 nm. The weight ratio between the p-type semiconductor material and the n-type semiconductor material included in the active layer (p/n ratio) is at most 99/1. The work function of the negative electrode side surface in contact with the active layer is lower than the absolute value of the LUMO energy level of the n-type semiconductor material.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority under 37 U.S.C. § 371 toInternational Patent Application No. PCT/JP2019/029404, filed Jul. 26,2019, which claims priority to and the benefit of Japanese PatentApplication No. 2018-145288, filed on Aug. 1, 2018. The contents ofthese applications are hereby incorporated by reference in theirentireties.

TECHNICAL FIELD

The present invention relates to a photoelectric conversion element,particularly a light detecting element.

BACKGROUND ART

The photoelectric conversion element has been attracting attention as avery useful device from the viewpoint of energy saving and reduction ofcarbon dioxide emissions, for example.

The photoelectric conversion element includes at least a pair ofelectrodes including a positive electrode and a negative electrode, andan active layer provided between the pair of electrodes. In thephotoelectric conversion element, one of the electrodes is made of atransparent or translucent material, and light is incident on the activelayer from the transparent or translucent electrode side. The energy(hυ) of light incident on the active layer generates electric charges(holes and electrons) in the active layer, the generated holes movetoward the positive electrode, and the electrons move toward thenegative electrode. Then, the electric charges that have reached thepositive electrode and the negative electrode are taken out of thephotoelectric conversion element via the electrodes.

Among the photoelectric conversion elements, particularly, a lightdetecting element has been used in an image sensor, various biometricauthentication devices, and the like, and requires sensitivity in adetection wavelength region, that is, a predetermined wavelength regiondepending on the application, and thus various studies have beenconducted in recent years.

In the related art, commonly used light detecting elements usually havesensitivity in a wide region from a visible light region to a nearinfrared region, and for example, in order to further increase thesensitivity in a predetermined detection wavelength region such as thenear infrared wavelength region, an optical member such as an opticalfilter that selectively blocks light having a wavelength outside thedetection wavelength region has been used (refer to Patent Document 1).

PRIOR ART DOCUMENTS Non-Patent Document

-   Patent Document 1: JP-A-2014-22675

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

However, in the light detecting element according to Patent Document 1,since additional components such as an optical member for realizing adesired function are indispensable, not only the structure becomescomplicated but also high sensitivity in a desired detection wavelengthregion cannot be obtained in some cases.

The present invention has been made in view of the above problems, andan object of the present invention is to provide a light detectingelement capable of improving sensitivity in a predetermined detectionwavelength region with a simpler configuration.

Means for Solving the Problems

As a result of diligent studies to solve the above problems, the presentinventors have found that the above problems can be solved if thefollowing requirements are satisfied, and have completed the presentinvention. That is, the present invention provides the following [1] to[8].

-   -   [1] A light detecting element including a positive electrode, a        negative electrode, and an active layer provided between the        positive electrode and the negative electrode and containing a        p-type semiconductor material and an n-type semiconductor        material,    -   wherein a thickness of the active layer is at least 800 nm,    -   a weight ratio (p/n ratio) of the p-type semiconductor material        to the n-type semiconductor material contained in the active        layer is at most 99/1, and    -   a work function of a surface in contact with the active layer on        the negative electrode side is lower than an absolute value of a        LUMO energy level of the n-type semiconductor material.    -   [2] The light detecting element according to [1], wherein        external quantum efficiency has a narrow peak in a near infrared        wavelength region.    -   [3] The light detecting element according to [2], wherein a full        width at half maximum of the narrow peak is at most less than        300 nm.    -   [4] The light detecting element according to any one of [1] to        [3], wherein the surface is a surface of an electron transport        layer provided between the negative electrode and the active        layer.    -   [5] The light detecting element according to any one of [1] to        [4], wherein the n-type semiconductor material is a fullerene        derivative.    -   [6] The light detecting element according to [5], wherein the        fullerene derivative is C70PCBM.    -   [7] The light detecting element according to any one of [2] to        [6], wherein in a visible light wavelength region, the external        quantum efficiency at the maximum absorption wavelength of the        active layer is at most 20% of the maximum value of the external        quantum efficiency of the narrow peak.    -   [8] An image sensor including the light detecting element        according to any one of [1] to [7].

Effect of the Invention

According to the present invention, it is possible to provide a lightdetecting element having high sensitivity in a predetermined wavelengthregion with a simpler configuration.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram schematically illustrating a photoelectricconversion element (light detecting element).

FIG. 2 is a diagram schematically illustrating a configuration exampleof an image detector.

FIG. 3 is a diagram schematically illustrating a configuration exampleof a fingerprint detector.

FIG. 4 is a graph illustrating an EQE spectrum of a light detectingelement and an absorption spectrum of an active layer.

FIG. 5 is a graph illustrating the EQE spectrum of the light detectingelement and the absorption spectrum of the active layer.

FIG. 6 is a graph illustrating the EQE spectrum of the light detectingelement and the absorption spectrum of the active layer.

FIG. 7 is a graph illustrating the EQE spectrum of the light detectingelement and the absorption spectrum of the active layer.

FIG. 8 is a graph illustrating the EQE spectrum of the light detectingelement and the absorption spectrum of the active layer.

FIG. 9 is a graph illustrating the EQE spectrum of the light detectingelement and the absorption spectrum of the active layer.

FIG. 10 is a graph illustrating the EQE spectrum of the light detectingelement and the absorption spectrum of the active layer.

FIG. 11 is a graph illustrating the EQE spectrum of the light detectingelement and the absorption spectrum of the active layer.

FIG. 12 is a graph illustrating the EQE spectrum of the light detectingelement.

MODE FOR CARRYING OUT THE INVENTION

Hereinafter, a photoelectric conversion element according to anembodiment of the present invention will be described with reference tothe drawings. Note that the drawings merely outline the shapes, sizes,and arrangements of components to the extent that the invention can beunderstood. The present invention is not limited to the followingdescription, and each component can be appropriately modified withoutdeparting from the gist of the present invention. Further, in theconfiguration according to the embodiment of the present invention, itis not always produced or used in the arrangement illustrated in thedrawings. In each of the drawings described below, the same componentsmay be given the same sign and the description thereof may be omitted.

Here, first, terms commonly used in the following description will bedescribed.

The “polymer compound” means a polymer having a molecular weightdistribution and having a polystyrene-equivalent number averagemolecular weight of 1×10³ or more and 1×10⁸ or less. Constituent unitscontained in the polymer compound are 100 mol % in total.

The “constituent unit” means a unit existing in one or more in a polymercompound.

A “hydrogen atom” may be a light hydrogen atom or a deuterium atom.

A “halogen atom” includes a fluorine atom, a chlorine atom, a bromineatom, and an iodine atom.

The meaning of “may have a substituent” includes a case where all thehydrogen atoms constituting the compound or group are unsubstituted, anda case where some or all of one or more hydrogen atoms are substitutedby the substituent.

Unless otherwise specified, the “alkyl group” may be linear, branched,or cyclic. The number of carbon atoms of the linear alkyl group isusually 1 to 50, preferably 1 to 30, and more preferably 1 to 20 withoutincluding the number of carbon atoms of the substituent. The number ofcarbon atoms of a branched or cyclic alkyl group is usually 3 to 50,preferably 3 to 30, and more preferably 4 to 20 without including thenumber of carbon atoms of the substituent.

The alkyl group may have a substituent. Specific examples of the alkylgroup include an alkyl group such as a methyl group, an ethyl group, ann-propyl group, an isopropyl group, an n-butyl group, an isobutyl group,a tert-butyl group, an n-pentyl group, an isoamyl group, a 2-ethylbutylgroup, an n-hexyl group, a cyclohexyl group, an n-heptyl group, acyclohexylmethyl group, a cyclohexylethyl group, an n-octyl group, a2-ethylhexyl group, a 3-n-propylheptyl group, an adamantyl group, ann-decyl group, a 3,7-dimethyloctyl group, a 2-ethyloctyl group, a2-n-hexyl-decyl group, an n-dodecyl group, a tetradecyl group, ahexadecyl group, an octadecyl group, and an eicosyl group; and an alkylgroup having a substituent such as a trifluoromethyl group, apentafluoroethyl group, a perfluorobutyl group, a perfluorohexyl group,a perfluorooctyl group, a 3-phenylpropyl group, a 3-(4-methylphenyl)propyl group, a 3-(3,5-di-n-hexylphenyl) propyl group, and a6-ethyloxyhexyl group.

An “aryl group” means a remaining atomic group obtained by removing onehydrogen atom directly bonded to a carbon atom constituting a ring froman aromatic hydrocarbon which may have a substituent.

The aryl group may have a substituent. Specific examples of the arylgroup include a phenyl group, a 1-naphthyl group, a 2-naphthyl group, a1-anthrasenyl group, a 2-anthrasenyl group, a 9-anthrasenyl group, a1-pyrenyl group, a 2-pyrenyl group, a 4-pyrenyl group, a 2-fluorenylgroup, a 3-fluorenyl group, a 4-fluorenyl group, a 2-phenylphenyl group,a 3-phenylphenyl group, a 4-phenylphenyl group, and a group having asubstituent such as an alkyl group, an alkoxy group, an aryl group, anda fluorine atom.

An “alkoxy group” may be linear, branched, or cyclic. The number ofcarbon atoms of the linear alkoxy group is usually 1 to 40 andpreferably 1 to 10 without including the number of carbon atoms of thesubstituent. The number of carbon atoms of the branched or cyclic alkoxygroup is usually 3 to 40 and preferably 4 to 10 without including thenumber of carbon atoms of the substituent.

The alkoxy group may have a substituent. Specific examples of the alkoxygroup include a methoxy group, an ethoxy group, an n-propyloxy group, anisopropyloxy group, an n-butyloxy group, an isobutyloxy group, atert-butyloxy group, an n-pentyloxy group, an n-hexyloxy group, acyclohexyloxy group, an n-heptyloxy group, an n-octyloxy group, a2-ethylhexyloxy group, an n-nonyloxy group, an n-decyloxy group, a3,7-dimethyloctyloxy group, and a lauryloxy group.

The number of carbon atoms of the “aryloxy group” is usually 6 to 60 andpreferably 6 to 48 without including the number of carbon atoms of thesubstituent.

The aryloxy group may have a substituent. Specific examples of thearyloxy group include a phenoxy group, a 1-naphthyloxy group, a2-naphthyloxy group, a 1-anthrasenyloxy group, a 9-anthrasenyloxy group,a 1-pyrenyloxy group, and a group having a substituent such as an alkylgroup, an alkoxy group, and a fluorine atom.

An “alkylthio group” may be linear, branched, or cyclic. The number ofcarbon atoms of the linear alkylthio group is usually 1 to 40 andpreferably 1 to 10 without including the number of carbon atoms of thesubstituent. The number of carbon atoms of the branched and cyclicalkylthio groups is usually 3 to 40 and preferably 4 to 10 withoutincluding the number of carbon atoms of the substituent.

The alkylthio group may have a substituent. Specific examples of thealkylthio group include a methylthio group, an ethylthio group, apropylthio group, an isopropylthio group, a butylthio group, anisobutylthio group, a tert-butylthio group, a pentylthio group, ahexylthio group, a cyclohexylthio group, a heptylthio group, anoctylthio group, a 2-ethylhexylthio group, a nonylthio group, adecylthio group, a 3,7-dimethyloctylthio group, a laurylthio group, anda trifluoromethylthio group.

The number of carbon atoms of an “arylthio group” is usually 6 to 60 andpreferably 6 to 48 without including the number of carbon atoms of thesubstituent.

The arylthio group may have a substituent. Examples of the arylthiogroup include a phenylthio group and a C1 to C12 alkyloxyphenylthiogroup (here, “C1 to C12” indicates that the group to be describedimmediately after that has 1 to 12 carbon atoms. The same applies to thefollowing), a C1 to C12 alkylphenylthio group, a 1-naphthylthio group, a2-naphthylthio group, and a pentafluorophenylthio group.

A “p-valent heterocyclic group” (p represents an integer of 1 or more)means a remaining atomic group excluding p hydrogen atoms among thehydrogen atoms directly bonded to a carbon atom or a hetero atomconstituting a ring from a heterocyclic compound that may have asubstituent. Among the p-valent heterocyclic groups, a “p-valentaromatic heterocyclic group” is preferable. The “p-valent aromaticheterocyclic group” means a remaining atomic group excluding p hydrogenatoms among the hydrogen atoms directly bonded to a carbon atom or ahetero atom constituting a ring from an aromatic heterocyclic compoundthat may have a substituent.

Examples of the substituent that the heterocyclic compound may haveinclude a halogen atom, an alkyl group, an aryl group, an alkoxy group,an aryloxy group, an alkylthio group, an arylthio group, a monovalentheterocyclic group, a substituted amino group, an acyl group, an imineresidue, an amide group, an acidimide group, a substituted oxycarbonylgroup, an alkenyl group, an alkynyl group, a cyano group, and a nitrogroup.

Examples of the aromatic heterocyclic compound include a compound inwhich an aromatic ring is fused to the heterocycle even if theheterocycle itself does not exhibit aromaticity in addition to thecompound in which the heterocycle itself exhibits aromaticity.

Among the aromatic heterocyclic compounds, specific examples of thecompound in which the heterocycle itself exhibits aromaticity includeoxadiazole, thiadiazole, thiazole, oxazol, thiophene, pyrrole,phosphole, furan, pyridine, pyrazine, pyrimidine, triazine, pyridazine,quinoline, isoquinolin, carbazole, and dibenzophosphol.

Among the aromatic heterocyclic compounds, specific examples ofcompounds in which the aromatic heterocycle itself does not exhibitaromaticity and the aromatic ring is fused to the heterocycle includephenoxazine, phenothiazine, dibenzoborol, dibenzosiror, and benzopyran.

The number of carbon atoms of the monovalent heterocyclic group isusually 2 to 60 and preferably 4 to 20 without including the number ofcarbon atoms of the substituent.

The monovalent heterocyclic group may have a substituent, and specificexamples of the monovalent heterocyclic group include a thienyl group, apyrrolyl group, a furyl group, a pyridyl group, a piperidyl group, aquinolyl group, an isoquinolyl group, a pyrimidinyl group, a triazinylgroup, and a group having a substituent such as an alkyl group and analkoxy group.

The “substituted amino group” means an amino group having a substituent.Examples of substituents that an amino group has include an alkyl group,an aryl group, and a monovalent heterocyclic group. As the substituent,an alkyl group, an aryl group, or a monovalent heterocyclic group ispreferable. The number of carbon atoms of the substituted amino group isusually 2 to 30.

Examples of the substituted amino group include a dialkylamino groupsuch as a dimethylamino group and a diethylamino group, a diarylaminogroup such as a diphenylamino group, a bis(4-methylphenyl) amino group,a bis(4-tert-butylphenyl) amino group, and abis(3,5-di-tert-butylphenyl) amino group.

The “acyl group” usually has about 2 to 20 carbon atoms, and preferably2 to 18 carbon atoms. Specific examples of the acyl group include anacetyl group, a propionyl group, a butyryl group, an isobutyryl group, apivaloyl group, a benzoyl group, a trifluoroacetyl group, and apentafluorobenzoyl group.

The “imine residue” means a remaining atomic group obtained by removingone hydrogen atom directly bonded to a carbon atom or a nitrogen atomforming a carbon atom-nitrogen atom double bond from an imine compound.The “imine compound” means an organic compound having a carbonatom-nitrogen atom double bond in a molecule. Examples of the iminecompound include aldimine, ketimine, and a compound in which thehydrogen atom bonded to the nitrogen atom constituting the carbonatom-nitrogen atom double bond in aldimine is replaced with an alkylgroup or the like.

The imine residue usually has about 2 to 20 carbon atoms, and preferably2 to 18 carbon atoms. Examples of the imine residue include groupsrepresented by the following structural formulas.

The “amide group” means a remaining atomic group obtained by removingone hydrogen atom bonded to a nitrogen atom from the amide. The numberof carbon atoms of the amide group is usually about 1 to 20 andpreferably 1 to 18. Specific examples of the amide group include aformamide group, an acetamido group, a propioamide group, a butyroamidegroup, a benzamide group, a trifluoroacetamide group, apentafluorobenzamide group, a diformamide group, a diacetamide group, adipropioamide group, a dibutyroamide group, a dibenzamide group, aditrifluoroacetamide group, and a dipentafluorobenzamide group.

The “acidimide group” means a remaining atomic group obtained byremoving one hydrogen atom bonded to a nitrogen atom from the acidimide.The number of carbon atoms of the acidimide group is usually about 4 to20. Specific examples of the acidimide group include a group representedby the following structural formulas.

The “substituted oxycarbonyl group” means a group represented byR′—O—(C═O)—.

Here, R′ represents an alkyl group, an aryl group, an arylalkyl group,or a monovalent heterocyclic group.

The substituted oxycarbonyl group usually has about 2 to 60 carbon atomsand preferably 2 to 48 carbon atoms.

Specific examples of the substituted oxycarbonyl group include amethoxycarbonyl group, an ethoxycarbonyl group, a propoxycarbonyl group,an isopropoxycarbonyl group, a butoxycarbonyl group, anisobutoxycarbonyl group, a tert-butoxycarbonyl group, apentyloxycarbonyl group, a hexyloxycarbonyl group, acyclohexyloxycarbonyl group, a heptyloxycarbonyl group, anoctyloxycarbonyl group, a 2-ethylhexyloxycarbonyl group, anonyloxycarbonyl group, a decyloxycarbonyl group, a3,7-dimethyloctyloxycarbonyl group, a dodecyloxycarbonyl group, atrifluoromethoxycarbonyl group, a pentafluoroethoxycarbonyl group, aperfluorobutoxycarbonyl group, a perfluorohexyloxycarbonyl group, aperfluorooctyloxycarbonyl group, a phenoxycarbonyl group, anaphthoxycarbonyl group, and a pyridyloxycarbonyl group.

The “alkenyl group” may be linear, branched, or cyclic. The number ofcarbon atoms of the linear alkenyl group is usually 2 to 30 andpreferably 3 to 20 without including the number of carbon atoms of thesubstituent. The number of carbon atoms of the branched or cyclicalkenyl group is usually 3 to 30 and preferably 4 to 20 withoutincluding the number of carbon atoms of the substituent.

The alkenyl group may have a substituent. Specific examples of thealkenyl group include a vinyl group, a 1-propenyl group, a 2-propenylgroup, a 2-butenyl group, a 3-butenyl group, a 3-pentenyl group, a4-pentenyl group, a 1-hexenyl group, a 5-hexenyl group, a 7-octenylgroup, and a group having a substituent such as an alkyl group and analkoxy group.

The “alkynyl group” may be linear, branched, or cyclic. The number ofcarbon atoms of the linear alkenyl group is usually 2 to 20 andpreferably 3 to 20 without including the number of carbon atoms of thesubstituent. The number of carbon atoms of the branched or cyclicalkenyl group is usually 4 to 30 and preferably 4 to 20 withoutincluding the number of carbon atoms of the substituent.

The alkynyl group may have a substituent. Specific examples of thealkynyl group include an ethynyl group, a 1-propynyl group, a 2-propynylgroup, a 2-butynyl group, a 3-butynyl group, a 3-pentynyl group, a4-pentynyl group, a 1-hexynyl group, a 5-hexynyl group, and a grouphaving a substituent such as an alkyl group and an alkoxy group.

[1. Light Detecting Element]

A light detecting element (photoelectric conversion element) accordingto the present embodiment includes a positive electrode, a negativeelectrode, and an active layer provided between the positive electrodeand the negative electrode, and containing a p-type semiconductormaterial and an n-type semiconductor material, in which a thickness ofthe active layer is at least 800 nm, a weight ratio (p/n ratio) of thep-type semiconductor material to the n-type semiconductor materialcontained in the active layer is at most 99/1, and a work function of asurface in contact with the active layer on the negative electrode sideis lower than an absolute value of a LUMO energy level of the n-typesemiconductor material.

Here, “LUMO” (Lowest Unoccupied Molecular Orbital) means the lowestempty orbital.

The LUMO level of n-type semiconductor materials can be estimated fromcyclic voltammetry (CV) measurement values. The CV measurement forevaluating the LUMO level can be performed, for example, according tothe method described in Advanced Materials, Vol. 18, 2006, pp. 789-794.

With reference to FIG. 1 , a configuration example of the lightdetecting element according to the present embodiment will be described.A configuration example of a light detecting element having a so-calledreverse laminated structure will be described.

FIG. 1 is a diagram schematically illustrating a light detecting elementaccording to an embodiment of the present invention.

As illustrated in FIG. 1 , the light detecting element 10 of the presentembodiment is provided on, for example, a support substrate 11. Thelight detecting element 10 includes a negative electrode 12 provided incontact with the support substrate 11, an electron transport layer 13provided in contact with the negative electrode 12, an active layer 14provided in contact with the electron transport layer 13, a holetransport layer 15 provided in contact with the active layer 14, and apositive electrode 16 provided in contact with the hole transport layer15. In this configuration example, a sealing substrate 17 provided incontact with the negative electrode is further provided.

Hereinafter, the components that can be contained in the light detectingelement of the present embodiment will be specifically described.

(Substrate)

The light detecting element is usually formed on a substrate (supportsubstrate or sealing substrate). A pair of electrodes, usually formed ofa negative electrode and a positive electrode, are formed on thissubstrate. A material of the substrate is not particularly limited aslong as it is a material that does not chemically change when forming alayer containing, particularly, an organic compound.

Examples of the material of the substrate include glass, plastic, apolymer film, and silicon. In a case of an opaque substrate, it ispreferable that an electrode (that is, the electrode on the side farfrom the opaque substrate) on the side opposite to the electrodeprovided on the opaque substrate side is a transparent or translucentelectrode.

(Electrode)

The light detecting element includes a pair of electrodes, a positiveelectrode and a negative electrode. At least one of the positiveelectrode and the negative electrode is preferably a transparent ortranslucent electrode in order to allow light to enter.

Examples of the material of the transparent or translucent electrodeinclude a conductive metal oxide film and a translucent metal thin film.Specific examples of the electrode material include conductive materialssuch as indium oxide, zinc oxide, tin oxide, and indium tin oxide (ITO),indium zinc oxide (IZO), and NESA, which are composites thereof, andgold, platinum, silver, and copper. As a transparent or translucentelectrode material, ITO, IZO, and tin oxide are preferable. Further, asthe electrode, a transparent conductive film using an organic compoundsuch as polyaniline and a derivative thereof, or polythiophene and aderivative thereof as a material may be used. The transparent ortranslucent electrode may be a positive electrode or a negativeelectrode.

If one of the pair of electrodes is transparent or translucent, theother electrode may be an electrode having low light transmittance.Examples of the material of the electrode having low light transmittanceinclude metal and a conductive polymer. Specific examples of material ofthe electrode having low light transmittance include metals such aslithium, sodium, potassium, rubidium, cesium, magnesium, calcium,strontium, barium, aluminum, scandium, vanadium, zinc, yttrium, indium,cerium, samarium, europium, terbium, and ytterbium, and alloys of two ormore of these, or alloys of one or more of these metals with one or moremetals selected from the group consisting of gold, silver, platinum,copper, manganese, titanium, cobalt, nickel, tungsten, and tin,graphite, a graphite interlayer compound, polyaniline and a derivativethereof, and polythiophene and a derivative thereof. Examples of thealloys include a magnesium-silver alloy, a magnesium-indium alloy, amagnesium-aluminum alloy, an indium-silver alloy, a lithium-aluminumalloy, a lithium-magnesium alloy, a lithium-indium alloy, and acalcium-aluminum alloy.

As a method for forming an electrode, any suitable forming method knownin the related art can be used. Examples of the method for forming anelectrode include a vacuum deposition method, a sputtering method, anion plating method, and a plating method.

(Active Layer)

The active layer contains a p-type semiconductor material(electron-donating compound) and an n-type semiconductor material(electron-accepting compound) (details of suitable p-type semiconductormaterial and n-type semiconductor material will be described later).Whether it is the p-type semiconductor material or the n-typesemiconductor material can be relatively determined from a HOMO energylevel or a LUMO energy level of the selected compound.

In the present embodiment, the thickness of the active layer is at least800 nm, preferably 800 nm or more and 10000 nm or less from theviewpoint of improving the sensitivity of the light detecting element ina predetermined wavelength region, particularly in the near infraredwavelength region (780 nm to 2500 nm), and it is more preferably 800 nmor more and 2000 nm or less from the viewpoint of producing an activelayer having a uniform thickness.

By adjusting the thickness of the active layer within the above range,the sensitivity of the light detecting element outside the predeterminedwavelength region, particularly outside the near infrared wavelengthregion having a wavelength of less than 780 nm can be specificallyreduced, and the sensitivity of the light detecting element in apredetermined narrow wavelength region, particularly in the narrowwavelength region of the near infrared wavelength region can be moreimproved.

The active layer includes a p-type semiconductor material and an n-typesemiconductor material.

In the light detecting element of the present embodiment, the externalquantum efficiency at the maximum absorption wavelength of the activelayer in the visible light wavelength region (wavelength 360 nm to 830nm) is preferably at most 20% with respect to the maximum value of theexternal quantum efficiency of the narrow peak, particularly, from theviewpoint of improving the sensitivity in a predetermined wavelengthregion, it is preferably set to at most 10%.

Specifically, in order for the external quantum efficiency (EQE) to havea narrow peak in a predetermined wavelength region, for example, a nearinfrared wavelength region, a p-type semiconductor material and/or ann-type semiconductor material contained in the active layer arepreferably selected so that the absorption peak of the active layer islocated in the vicinity of the near infrared wavelength region. At thistime, it is preferably selected so that the external quantum efficiencyat the absorption peak wavelength on the near infrared wavelength regionside (particularly in the vicinity of the near infrared wavelengthregion) in the visible light wavelength region of the p-typesemiconductor material and/or the n-type semiconductor material is atmost 20% when the maximum value of the external quantum efficiency in anarrow peak is 100%. In other words, the p-type semiconductor materialand/or the n-type semiconductor material contained in the active layeris preferably selected so as to be at the external quantum efficiency,for example, it is preferable that the external quantum efficiency atthe starting point (lowest hem edge) on the low wavelength side of themountain-shaped narrow peak that occurs in the near infrared wavelengthregion is at most 20% when the maximum value of the external quantumefficiency at the narrow peak is 100%.

Here, the “external quantum efficiency (EQE)” specifically refers to avalue indicating a number of electrons, by a ratio (%), which can betaken out of the light detecting element, among the electrons generatedfor the number of photons with which the light detecting element isirradiated.

Further, the “narrow peak” means, for example, a mountain-shaped peak ofexternal quantum efficiency that occurs in the near infrared wavelengthregion and has a predetermined full width at half maximum, which will bedescribed later.

The active layer can preferably be formed by a coating method. Detailsof the p-type semiconductor material and the n-type semiconductormaterial that can be contained in the active layer and the method forforming the active layer will be described later.

(Intermediate Layer)

As illustrated in FIG. 1 , the light detecting element of the presentembodiment preferably includes an intermediate layer such as a chargetransport layer (electron transport layer, hole transport layer,electron injection layer, hole injection layer) as a component forimproving the characteristics.

As the material used for such an intermediate layer, for example, anysuitable material known in the related art that contributes to thetransfer of electric charge in the layer constituting the lightdetecting element can be used. Examples of the material of theintermediate layer include halides of alkali metals or alkaline earthmetals such as lithium fluoride, and oxides such as molybdenum oxide.

Examples of the materials used for the intermediate layer include fineparticles of inorganic oxides (semiconductors) such as titanium oxideand zinc oxide, and a mixture (PEDOT:PSS) of PEDOT(poly(3,4-ethylenedioxythiophene)) and PSS (poly(4-(styrene sulfonate)).

As illustrated in FIG. 1 , the light detecting element of the presentembodiment may include an electron transport layer as the intermediatelayer between the negative electrode and the active layer. The electrontransport layer has a function of transporting electrons from the activelayer to the negative electrode. The electron transport layer may be incontact with the negative electrode. The electron transport layer may bein contact with the active layer.

The electron transport layer provided in contact with the negativeelectrode may be particularly referred to as an electron injectionlayer. The electron transport layer (electron injection layer) providedin contact with the negative electrode has a function of promoting theinjection of electrons generated in the active layer into the negativeelectrode.

The electron transport layer contains an electron transport material.Examples of the electron transport material include polyalkyleneimineand a derivative thereof, a polymer compound having a fluorenestructure, and metal oxide.

The electron transport layer preferably contains polyalkyleneimine or aderivative thereof, or metal oxide.

Examples of polyalkyleneimine and a derivative thereof includealkyleneimine having 2 to 8 carbon atoms such as ethyleneimine,propyleneimine, butyleneimine, dimethylethyleneimine, pentyleneimine,hexyleneimine, heptyleneimine, and octyleneimine, particularly, polymersobtained by polymerizing one or two or more of alkyleneimines having 2to 4 carbon atoms by a common method, and a polymers that are chemicallymodified by reacting them with various compounds. As thepolyalkyleneimine and a derivative thereof, polyethyleneimine ethoxylate(PEIE: ethoxylated polyethyleneimine) containing polyethyleneimine (PEI)and polyalkyleneimine as a main chain, and ethylene oxide which is amodified product added to nitrogen atoms in the main chain ispreferable.

Examples of the polymer compound having a fluorene structure includepoly[(9,9-bis(3′-(N,N-dimethylamino)propyl)-2,7-fluorene)-ortho-2,7-(9,9′-dioctylfluorene)] (PFN) andPFN-P2.

Examples of the metal oxide include zinc oxide, gallium-doped zincoxide, aluminum-doped zinc oxide, titanium oxide, and niobium oxide. Asthe metal oxide, a metal oxide containing zinc is preferable, and zincoxide is particularly preferable.

Examples of other electron transport materials includepoly(4-vinylphenol) and perylene diimide.

In the light detecting element of the present invention, the workfunction of the surface in contact with the active layer on the negativeelectrode side is lower than the absolute value of the LUMO energy levelof the n-type semiconductor material contained in the active layer. Inother words, a difference between the work function of the surface incontact with the active layer on the negative electrode side and theabsolute value of the LUMO energy level of the n-type semiconductormaterial contained in the active layer is set to be a negative value.

Here, specific examples of the surface in contact with the active layeron the negative electrode side include the surface of the negativeelectrode and the surface of the electron transport layer providedbetween the negative electrode and the active layer. For example, in acase where the intermediate layer such as the electron transport layer(electron injection layer) is not formed, the “surface in contact withthe active layer on the negative electrode side” is the surface of thenegative electrode, and in a case where the electron transport layer(electron injection layer) is used as the intermediate layer, the“surface in contact with the active layer on the negative electrodeside” is the surface of the electron transport layer (electron injectionlayer).

The work function of the surface in contact with the active layer on thenegative electrode side can be determined by appropriately changing thematerial and producing conditions of the structure constituting thesurface (surface), and can be adjusted to obtain the desired value byperforming any suitable surface treatment known in the related, forexample, a physical treatment such as a corona discharge treatment, anoxygen plasma treatment, or an ultraviolet ozone treatment, a chemicaltreatment such as a cleaning treatment using water or organic solvent oran acid cleaning treatment, with respect to the structure constitutingthe surface.

The work function can be evaluated (measured) using, for example, aknown Kelvin probe device in the related art (for example, FAC-2,available from RIKEN KEIKI Co., Ltd.) and gold (WF: 5.1 eV) as areference sample for calibration.

As illustrated in FIG. 1 , the light detecting element of the presentembodiment may include a hole transport layer between the positiveelectrode and the active layer. The hole transport layer has a functionof transporting holes from the active layer to the electrode. Since thehole transport layer has a function of blocking the flow of electrons tothe electrode, it is sometimes called an electron block layer.

The hole transport layer provided in contact with the positive electrodemay be particularly referred to as a hole injection layer. The holetransport layer (hole injection layer) provided in contact with thepositive electrode has a function of promoting the injection of holesinto the positive electrode.

The hole transport layer contains a hole transport material. Examples ofthe hole transport material include polythiophene and a derivativethereof, an aromatic amine compound, a polymer compound containing aconstituent unit having an aromatic amine residue, CuSCN, CuI, NiO, andmolybdenum oxide (MoO3).

The intermediate layer can be formed by the same coating method as thatfor the active layer.

The light detecting element according to the present embodiment isprovided on a substrate, and preferably has a so-called reverselaminated structure in which the intermediate layer is an electrontransport layer and a hole transport layer, and the negative electrode,the electron transport layer, the active layer, the hole transportlayer, and the positive electrode are laminated in this order so as tobe in contact with each other.

(Other)

The light detecting element of the present embodiment can be sealed by asealing member such as a sealing substrate or a sealing material.Examples of the sealing member include a combination of cover glasshaving a recess and a sealing material.

The sealing member may have a layer structure of one or more layers.Therefore, as an example of the sealing member, a layer structure suchas a gas barrier layer and a gas barrier film can be furtherexemplified.

The layer structure of the sealing member is preferably formed of amaterial having a property of blocking water (water vapor barrierproperty) or a property of blocking oxygen (oxygen barrier property).Examples of suitable materials as materials having a layer structureinclude organic materials such as resins of polyethylene trifluoride,polychlorotrifluoroethylene (PCTFE), polyimide, polycarbonate,polyethylene terephthalate, alicyclic polyolefin, and an ethylene-vinylalcohol copolymer; and inorganic materials such as silicon oxide,silicon nitride, aluminum oxide, and diamond-like carbon.

According to the present invention, a thickness of the active layer isat least 800 nm, a weight ratio (p/n ratio) of the p-type semiconductormaterial to the n-type semiconductor material contained in the activelayer is at most 99/1, and a work function of a surface in contact withthe active layer on the negative electrode side is lower than anabsolute value of a LUMO energy level of the n-type semiconductormaterial.

In the general photoelectric conversion element, in order to promote theextraction of electrons generated in the active layer, a differencebetween the work function of the surface in contact with the activelayer on the negative electrode side and the LUMO energy level of then-type semiconductor material contained in the active layer is set to bea positive value.

However, in the present invention, as described above, an appropriateenergy barrier is provided at the interface of the active layer on thenegative electrode side to prevent electrons from being taken out to thenegative electrode.

As a result, the electrons are accumulated in the vicinity of theinterface of the active layer on the negative electrode side, and theaccumulated electrons disappear due to recombination with holes.

On the other hand, the electrons generated at a wavelength at which thelight absorption of the active layer is low can be taken out to thenegative electrode without being accumulated at the interface due to thelow electron density.

As a result, the external quantum efficiency caused by the p-typesemiconductor material and the n-type semiconductor material is reduced,and the external quantum efficiency has, for example, a narrow peak inthe near infrared wavelength region, so that a light detecting elementhaving a specific narrow band sensitivity characteristics can berealized in the near infrared wavelength region.

In the present embodiment, specifically, the full width at half maximumof the mountain-shaped peak of the external quantum efficiency generatedin the near infrared wavelength region is obtained under the conditionthat a bias voltage of −2 V is applied to the light detecting element.Since the full width at half maximum can enhance the selectivity of theabsorption wavelength, it is preferably less than at most 300 nm, andmore preferably 100 nm or less.

With such a configuration, it is possible to provide a light detectingelement having high sensitivity in a predetermined wavelength region,specifically, for example, a near infrared wavelength region, with asimpler configuration without using an optical member such as an opticalfilm.

<Application Example of Light Detecting Element>

The light detecting element according to the embodiment of the presentinvention described above is suitably applied to a detector provided invarious electronic devices such as a workstation, a personal computer, apersonal digital assistant, an access control system, a digital camera,and a medical device.

The light detecting element of the present invention can be suitablyapplied to, for example, an image detector (image sensor) for asolid-state imaging device such as an X-ray imaging device and a CMOSimage sensor; a detector that detects a predetermined feature of a partof a living body such as a fingerprint detector, a face detector, a veindetector, and an iris detector; and a detector of an optical biosensorsuch as a pulse oximeter, which are included in the above-exemplifiedelectronic device.

Hereinafter, among the detectors to which the light detecting elementaccording to the embodiment of the present invention can be suitablyapplied, configuration examples of the image detector for a solid-stateimaging device and the fingerprint detector for a biometric informationauthentication device (fingerprint authenticating device) will bedescribed with reference to the drawings.

<Image Detector>

FIG. 2 is a diagram schematically illustrating a configuration exampleof an image detector for a solid-state imaging device.

An image detector 1 is provided with a CMOS transistor substrate 20, aninterlayer insulating film 30 provided so as to cover the CMOStransistor substrate 20, and a light detecting element 10 according tothe embodiment of the present invention, provided on the interlayerinsulating film 30, an interlayer wiring portion 32 that is provided soas to penetrate the interlayer insulating film 30 and electricallyconnects the CMOS transistor substrate 20 and the light detectingelement 10 to each other, a sealing layer 40 provided so as to cover thelight detecting element 10, and a color filter 50 provided on thesealing layer.

The CMOS transistor substrate 20 includes any suitable configurationknown in the related art in an aspect corresponding to the design.

The CMOS transistor substrate 20 includes a transistor, capacitors, andthe like formed within the thickness of the substrate, and includesfunctional elements such as a CMOS transistor circuit (MOS transistorcircuit) for realizing various functions.

Examples of the functional element include a floating diffusion, a resettransistor, an output transistor, and a selection transistor.

A signal readout circuit and the like are built in the CMOS transistorsubstrate 20 by such functional elements and wiring.

The interlayer insulating film 30 can be formed of any suitableinsulating material known in the related art such as silicon oxide or aninsulating resin. The interlayer wiring portion 32 can be formed of, forexample, any suitable conductive material (wiring material) known in therelated art such as copper and tungsten. The interlayer wiring portion32 may be, for example, an in-hole wiring formed at the same time as theformation of the wiring layer, or an embedded plug formed separatelyfrom the wiring layer.

The sealing layer 40 can be formed of any suitable materials known inthe related art under the conditions that the penetration of harmfulsubstances such as oxygen and water that may functionally deterioratethe light detecting element 10 can be prevented or suppressed. Thesealing layer 40 may be formed of the sealing substrate 17 describedabove.

As the color filter 50, for example, a primary color filter which ismade of any suitable material known in the related art and whichcorresponds to the design of the image detector 1 can be used. Further,as the color filter 50, a complementary color filter capable of reducingthe thickness as compared with the primary color filter can also beused. Examples of the complementary color filters include color filtersthat combine three types of (yellow, cyan, and magenta), three types of(yellow, cyan, and transparent), three types of (yellow, transparent,and magenta), and three types of (transparent, cyan, and magenta) can beused. Assuming that these are subject to the ability to generate colorimage data, any suitable arrangement can be made corresponding to thedesign of the light detecting element 10 and the CMOS transistorsubstrate 20.

The light received by the photoelectric conversion element (lightdetecting element) 10 via the color filter 50 is converted into anelectric signal according to the amount of light received by the lightdetecting element 10, and is output as a light receiving signal, thatis, an electric signal corresponding to an image pickup target, outsidethe light detecting element 10.

Next, the received light signal output from the light detecting element10 is input to the CMOS transistor substrate 20 via the interlayerwiring portion 32, and is read out by the signal readout circuit builtin the CMOS transistor substrate 20, and signal processing is performedby a further optional suitable known functional unit in the related art(not shown) so as to generate the image information based on the imagetarget.

<Fingerprint Detector>

FIG. 3 is a diagram schematically illustrating a configuration exampleof a fingerprint detector integrated with the display device.

The display device 2 of a personal digital assistant is provided with afingerprint detector 100 including the light detecting element 10according to the embodiment of the present invention as a main componentand a display panel unit 200 that is provided on the fingerprintdetector 100, and displays a predetermined image.

In this configuration example, the fingerprint detector 100 is providedin a region that substantially coincides with a display region 200 a ofthe display panel unit 200. In other words, the display panel unit 200is integrally laminated above the fingerprint detector 100.

In a case where the fingerprint detection is performed only in a partregion of the display region 200 a, the fingerprint detector 100 may beprovided corresponding to only the part region of the display region 200a.

The fingerprint detector 100 includes the light detecting element 10according to the embodiment of the present invention as a functionalunit that performs an essential function. The fingerprint detector 100can be provided with any suitable member known in the related art, suchas a protection film (not shown), a support substrate, a sealingsubstrate, a sealing member, a barrier film, a bandpass filter, and aninfrared cut film in an aspect corresponding to the design of obtainingdesired characteristics. For the fingerprint detector 100, theconfiguration of the image detector as described above can also beadopted.

The light detecting element 10 may be included in any aspect within thedisplay region 200 a. For example, a plurality of light detectingelements 10 may be arranged in a matrix.

As described above, the light detecting element 10 is provided on thesupport substrate 11 or the sealing substrate, and the support substrate11 is provided with electrodes (positive electrode or negativeelectrode) in a matrix, for example.

The light received by the light detecting element 10 is converted intoan electric signal according to the amount of light received by thephotoelectric conversion element 10, and is output as a light receivingsignal, that is, an electric signal corresponding to a capturedfingerprint, outside the light detecting element 10.

In this configuration example, the display panel unit 200 is configuredas an organic electroluminescence display panel (organic EL displaypanel) including a touch sensor panel. The display panel unit 200 may beconfigured of, for example, instead of the organic EL display panel, adisplay panel having an any suitable configuration known in the relatedart, such as a liquid crystal display panel including a light sourcesuch as a backlight.

The display panel unit 200 is provided on the fingerprint detector 100as described above. The display panel unit 200 includes an organicelectroluminescence element (organic EL element) 220 as a functionalunit that performs an essential function. The display panel unit 200 maybe further provided with any suitable substrate (support substrate 210or sealing substrate 240) known in the related art, such as a glasssubstrate, a sealing member, a barrier film, a polarizing plate such asa circular polarizing plate, and any suitable member known in therelated art, such as a touch sensor panel 230 in an aspect correspondingto the desired characteristics.

In the configuration example described above, the organic EL element 220is used as a light source for pixels in the display region 200 a, and isalso used as a light source for capturing a fingerprint in thefingerprint detector 100.

Here, an operation of the fingerprint detector 100 will be brieflydescribed.

When performing fingerprint authentication, the fingerprint detector 100detects a fingerprint using the light emitted from the organic ELelement 220 of the display panel unit 200. Specifically, the lightemitted from the organic EL element 220 passes through the componentexisting between the organic EL element 220 and the light detectingelement 10 of the fingerprint detector 100, and is reflected by skin(finger surface) of the fingertips of the fingers placed so as to be incontact with the surface of the display panel unit 200 within thedisplay region 200 a. At least a part of the light reflected by thefinger surface passes through the components existing between them andis received by the photoelectric conversion element 10, and is convertedinto an electric signal corresponding to the amount of light received bythe photoelectric conversion element 10. Then, image information aboutthe fingerprint on the finger surface is formed of the convertedelectric signals.

The personal digital assistant provided with the display device 2performs fingerprint authentication by comparing the obtained imageinformation with the fingerprint data for fingerprint authenticationrecorded in advance by any suitable step known in the related art.

Since the light detecting element of the present embodiment has a narrowpeak of external quantum efficiency particularly in the near infraredwavelength region, as compared with the light detecting element in therelated art having sensitivity in a wide range of the visible lightwavelength region, for example, during the operation, the influence of adisturbance factor such as light caused by the external environment canbe made smaller, and the illuminance dependence on illumination is alsosmall. Therefore, according to the light detecting element of thepresent embodiment, a clearer image can be stably obtained, andtherefore, it can be particularly preferably applied to an image sensorincluding a fingerprint detector having the above configuration.

[2. Method for Producing Light Detecting Element]

The method for producing the light detecting element of the presentembodiment is not particularly limited. The light detecting element canbe produced by a forming method suitable for the material selected forforming each component.

Hereinafter, as an embodiment of the present invention, a method forproducing a light detecting element provided on a substrate (supportsubstrate) and having a configuration in which a negative electrode, anelectron transport layer, an active layer, a hole transport layer, and apositive electrode are in contact with each other in this order will bedescribed.

(Step of Preparing Substrate)

In this step, a support substrate provided with a negative electrode isprepared.

A method of providing the negative electrode on the support substrate isnot particularly limited. The negative electrode can be formed, forexample, by forming the above-exemplified material on the supportsubstrate made of the materials as described above by a vacuumdeposition method, a sputtering method, an ion plating method, a platingmethod, or the like.

Further, a substrate provided with a thin film formed of the material ofthe electrode as described above is available from the market, and ifnecessary, the negative electrode is formed by patterning a conductivethin film, thereby preparing a support substrate provided with thenegative electrode.

(Step of Forming Electron Transport Layer)

A method for producing the light detecting element may include a step offorming an electron transport layer (electron injection layer) providedbetween the active layer and the negative electrode as an intermediatelayer.

Specifically, the method for producing the light detecting element ofthe present embodiment may further include a step of forming an electrontransport layer after the step of preparing a support substrate providedwith a negative electrode and before a step of forming an active layer.

A method for forming an electron transport layer is not particularlylimited. From the viewpoint of more simplifying the step of forming theelectron transport layer, it is preferable to form the electrontransport layer by a coating method. That is, it is preferable thatbefore the formation of the active layer and after the formation of thenegative electrode, a coating liquid containing an electron transportmaterial and a solvent, which will be described later, is applied ontothe negative electrode, and the solvent is removed, if necessary, byperforming a drying treatment (heat treatment) so as to form theelectron transport layer.

The electron transport material for forming the electron transport layermay be an organic compound or an inorganic compound.

The electron transport material which is an organic compound may be alow molecular weight organic compound or a high molecular weight organiccompound.

Examples of the electron transport material that is a low molecularweight organic compound include an oxadiazole derivative,anthracinodimethane and a derivative thereof, benzoquinone and aderivative thereof, naphthoquinone and a derivative thereof,anthraquinone and a derivative thereof, tetracyanoanthraquinodimethaneand a derivative thereof, a fluorenone derivative,diphenyldicyanoethylene and a derivative thereof, a diphenoquinonederivative, 8-hydroxyquinoline and a metal complex of derivativethereof, polyquinolin and a derivative thereof, polyquinoxaline and aderivative thereof, polyfluorene and a derivative thereof, fullerenessuch as C60 fullerene and a derivative thereof, and a phenanthrenederivative such as bathocuproine.

Examples of the electron transport material which is the polymer organiccompound include polyvinylcarbazole and a derivative thereof, polysilaneand a derivative thereof, a polysiloxane derivative having an aromaticamine structure in a side chain or main chain, polyaniline and aderivative thereof, polythiophene and a derivative thereof, polypyrroleand a derivative thereof, polyphenylene vinylene and a derivativethereof, polythienylene vinylene and a derivative thereof, andpolyfluorene and a derivative thereof.

Examples of the electron transport material that is an inorganiccompound include zinc oxide, titanium oxide, zirconium oxide, tin oxide,indium oxide, GZO (gallium-doped zinc oxide), ATO (antimony-doped tinoxide), and AZO (aluminum-doped zinc oxide). Among these, zinc oxide,gallium-doped zinc oxide, or aluminum-doped zinc oxide is preferable.When forming the electron transport layer, it is preferable to form theelectron transport layer by using a coating liquid containing granularzinc oxide, gallium-doped zinc oxide, or aluminum-doped zinc oxide. Assuch an electron transport material, it is preferable to usenanoparticles of zinc oxide, nanoparticles of gallium-doped zinc oxide,or nanoparticles of aluminum-doped zinc oxide, and it is more preferableto form the electron transport layer using an electron transportmaterial consisting only of nanoparticles of zinc oxide, nanoparticlesof gallium-doped zinc oxide, or nanoparticles of aluminum-doped zincoxide.

The sphere-equivalent average particle size of the nanoparticles of zincoxide, the nanoparticles of the gallium-doped zinc oxide, and thenanoparticles of aluminum-doped zinc oxide is preferably 1 nm to 1000 nmand more preferably 10 nm to 100 nm. The average particle size can bemeasured by, for example, a laser light scattering method and an X-raydiffraction method.

In the method for producing a light detecting element of the presentembodiment, a step of forming an electron transport layer preferablyincludes a step of forming an electron transport layer by applying acoating liquid containing PEIE and zinc oxide.

Examples of the solvent contained in the coating liquid containing theelectron transport material include water, alcohol, ketone, andhydrocarbon. Specific examples of the alcohol include methanol, ethanol,isopropanol, butanol, ethylene glycol, propylene glycol, butoxyethanol,and methoxybutanol. Specific examples of the ketone include acetone,methyl ethyl ketone, methyl isobutyl ketone, 2-heptanone, andcyclohexanone. Specific examples of the hydrocarbon include n-pentane,cyclohexane, n-hexane, benzene, toluene, xylene, tetralin,chlorobenzene, and orthodichlorobenzene. The coating liquid may containone kind of solvent alone, may contain two or more kinds of solvents,and may contain two or more kinds of the above-described solvents.

The coating liquid used in the coating method for forming the electrontransport layer may be a dispersion liquid such as an emulsion (emulsionliquid) or a suspension (suspension). The coating liquid is preferably acoating liquid that causes less damage to the layer (active layer, orthe like) to which the coating liquid is applied, and specifically, acoating liquid that is difficult to dissolve the layer (active layer, orthe like) to which the coating liquid is applied.

The step of forming the electron transport layer is performed by acoating method, and by adjusting the size (particle size, molecularweight, or the like in a case of a polymer compound) of the electrontransport material to be used, the work function of the surface incontact with the active layer of the electron transport layer can beadjusted to any suitable range. Further, in a case where the coatingmethod is the spin coating method, the work function of the surface ofthe electron transport layer in contact with the active layer can beadjusted to any suitable range by adjusting the characteristics of thecoating liquid such as the concentration of the components in thecoating liquid used (viscosity of the coating liquid) and theimplementation conditions such as the spin rotation speed, the rotationtime, and the drying (heating) conditions.

(Step of Forming Active Layer)

The active layer, which is a main component of the photoelectricconversion element of the present embodiment, can be produced by acoating method using a coating liquid (ink).

Hereinafter, a step (i) and a step (ii) included in the step of formingthe active layer, which is a main component of the photoelectricconversion element of the present invention, will be described.

(Step (i))

As a method for applying a coating liquid to a coating target, anysuitable coating method can be used.

As the coating method, a slit coating method, a knife coating method, aspin coating method, a micro gravure coating method, a gravure coatingmethod, a bar coating method, an ink jet printing method, a nozzlecoating method, or a capillary coating method is preferable, and theslit coating method, the spin coating method, the capillary coat method,or the bar coat method is more preferable, and the slit coat method orthe spin coating method is further preferable.

A coating liquid for forming an active layer is applied to a coatingtarget selected according to the photoelectric conversion element andthe producing method thereof. The coating liquid for forming an activelayer can be applied to the functional layer of the photoelectricconversion element, in which the active layer can exist, in the step ofproducing the photoelectric conversion element. Therefore, the coatingtarget of the coating liquid for forming an active layer differsdepending on the layer configuration of the photoelectric conversionelement to be produced and the order of layer formation. For example, ina case where it has a layer configuration in which the photoelectricconversion element is provided on the substrate, and the positiveelectrode, the hole transport layer, the active layer, the electrontransport layer, and the negative electrode are laminated, and the layerdescribed on the right side is formed first, the coating target of thecoating liquid for forming an active layer is the electron transportlayer. In addition, in a case where it has a layer configuration inwhich the photoelectric conversion element is provided on the substrate,and the negative electrode, the electron transport layer, the activelayer, the hole transport layer, and the positive electrode arelaminated, and the layer described on the right side is formed first,the coating target of the coating liquid for forming an active layer isthe hole transport layer.

(Step (ii))

Any suitable method can be used as a method for removing the solventfrom the coating film of the coating liquid, that is, a method forremoving the solvent and solidifying the coating film. Examples of themethod for removing the solvent include a method for direct heatingusing a hot plate, and a drying method such as a hot air drying method,an infrared heating drying method, a flash lamp annealing drying method,and a vacuum drying method.

The thickness of the active layer can be set to a desired thickness byappropriately adjusting the solid content concentration in the coatingliquid and the conditions of the above step (i) and/or step (ii).

Specifically, for example, in a case where the coating method is theknife coating method, the thickness of the active layer can be adjustedto an any suitable thickness by adjusting the characteristic conditionsof the coating liquid such as the concentration (viscosity of thecoating liquid) of the components in the coating liquid to be used, andvarious implementation conditions in the knife coater method.

For example, in order to adjust the thickness of the active layer in thedirection of increasing the thickness, the concentration of thecomponent in the coating liquid is more increased and/or a gap betweenthe surface to be coated and the blade of the knife in the knife coatingmethod may be widened so that the coating speed is more increased.

The step of forming the active layer may include other steps in additionto the steps (i) and (ii), provided that the object and effect of thepresent invention are not impaired.

The method for producing the light detecting element may be a method forproducing a light detecting element including a plurality of activelayers, or a method in which the steps (i) and (ii) are repeated aplurality of times.

The coating liquid for forming an active layer may be a solution, or maybe a dispersion liquid such as a dispersion liquid, an emulsion(emulsion liquid), or a suspension (suspension). The coating liquid forforming an active layer according to the present embodiment contains ap-type semiconductor material, an n-type semiconductor material, and asolvent. Hereinafter, the components of the coating liquid for formingan active layer will be described.

(p-Type Semiconductor Material)

The p-type semiconductor material may be a low molecular weight compoundor a polymer compound.

Examples of the p-type semiconductor material which is the low molecularweight compound include phthalocyanine, metallic phthalocyanine,porphyrin, metallic porphyrin, oligothiophene, tetracene, pentacene, andrubrene.

In a case where the p-type semiconductor material is a polymer compound,the polymer compound has a predetermined polystyrene-equivalent weightaverage molecular weight.

Here, the polystyrene-equivalent weight average molecular weight means aweight average molecular weight calculated using a standard polystyrenesample using gel permeation chromatography (GPC).

The polystyrene-equivalent weight average molecular weight of the p-typesemiconductor material is preferably 20000 or more and 200000 or less,more preferably 30000 or more and 180000 or less, and further preferably40000 or more and 150000 or less from the viewpoint of solubility in asolvent.

Examples of the p-type semiconductor material which is the polymercompound include polyvinylcarbazole and a derivative thereof, polysilaneand a derivative thereof, a polysiloxane derivative having an aromaticamine structure in a side chain or main chain, polyaniline and aderivative thereof, polythiophene and a derivative thereof, polypyrroleand a derivative thereof, polyphenylene vinylene and a derivativethereof, polythienylene vinylene and a derivative thereof, andpolyfluorene and a derivative thereof.

The p-type semiconductor material, which is the polymer compound, ispreferably a polymer compound containing a constituent unit having athiophene skeleton.

The p-type semiconductor material is preferably a polymer compoundcontaining a constituent unit represented by the following Formula (I)and/or a constituent unit represented by the following Formula (II).

In Formula (I), Ar¹ and Ar² represent trivalent aromatic heterocyclicgroups, and Z represents groups represented by the following Formulas(Z-1) to (Z-7).

In Formula (II), Ar³ represents a divalent aromatic heterocyclic group.

In Formulas (Z-1) to (Z-7), R is a hydrogen atom, a halogen atom, analkyl group, an aryl group, an alkoxy group, an aryloxy group, analkylthio group, an arylthio group, a monovalent heterocyclic group, asubstituted amino group, an acyl group, an imine residue, an amidegroup, an acidimide group, a substituted oxycarbonyl group, an alkenylgroup, an alkynyl group, a cyano group, or a nitro group. In a casewhere there are two Rs in each of the Formulas (Z-1) to (Z-7), the twoRs may be the same or different from each other.

The constituent unit represented by Formula (I) is preferably theconstituent unit represented by the following Formula (I-1).

In Formula (I-1), Z has the same meaning as described above.

Examples of the constituent unit represented by Formula (I-1) includeconstituent units represented by the following Formulas (501) to (505).

In the Formulas (501) to (505), R has the same meaning as describedabove. In a case where there are two Rs, the two Rs may be the same ordifferent from each other.

The number of carbon atoms of the divalent aromatic heterocyclic grouprepresented by Ar³ is usually 2 to 60, preferably 4 to 60, and morepreferably 4 to 20. The divalent aromatic heterocyclic group representedby Ar³ may have a substituent. Examples of substituents that thedivalent aromatic heterocyclic group represented by Ar³ may have includea halogen atom, an alkyl group, an aryl group, an alkoxy group, anaryloxy group, an alkylthio group, an arylthio group, a monovalentheterocyclic group, a substituted amino group, an acyl group, an imineresidue, an amide group, an acidimide group, a substituted oxycarbonylgroup, an alkenyl group, an alkynyl group, a cyano group, and a nitrogroup.

Examples of the divalent aromatic heterocyclic group represented by Arainclude groups represented by the following Formulas (101) to (185).

In the Formulas (101) to (185), R has the same meaning as describedabove. In a case where there are a plurality of Rs, the plurality of Rsmay be the same or different from each other.

As the constituent unit represented by the Formula (II), constituentunits represented by the following Formulas (II-1) to (II-6) arepreferable.

In Formulas (II-1) to (II-6), X¹ and X² each independently represent anoxygen atom or a sulfur atom, and R has the same meaning as describedabove. In a case where there are a plurality of Rs, the plurality of Rsmay be the same or different from each other.

From the viewpoint of availability of the raw material compound, it ispreferable that both X¹ and X² in the Formulas (II-1) to (II-6) aresulfur atoms.

The polymer compound which is the p-type semiconductor material may havetwo or more kinds of constituent units of Formula (I), and may have twoor more kinds of constituent units of Formula (II).

In order to improve the solubility in the solvent, the polymer compoundwhich is the p-type semiconductor material may have a constituent unitrepresented by the following Formula (III).

In Formula (III), Ar⁴ represents an arylene group.

The arylene group represented by Ar⁴ means a remaining atomic groupobtained by removing two hydrogen atoms from the aromatic hydrocarbonwhich may have a substituent. Aromatic hydrocarbons also includecompounds in which two or more selected from the group consisting of acompound having a fused ring, an independent benzene ring, and a fusedring are bonded directly or via a divalent group such as a vinylenegroup.

Examples of the substituents that the aromatic hydrocarbon may haveinclude the same substituents as those exemplified as the substituentsthat the heterocyclic compound may have.

The number of carbon atoms in a portion of the arylene group excludingthe substituent is usually 6 to 60, and preferably 6 to 20. The numberof carbon atoms of the arylene group including the substituent isusually about 6 to 100.

Examples of the arylene group include a phenylene group (for example,the following Formulas 1 to 3), a naphthalene-diyl group (for example,the following Formulas 4 to 13), an anthracene-diyl group (for example,the following Formulas 14 to 19), a biphenyl-diyl group (for example,the following Formulas 20 to 25), a terphenyl-diyl group (for example,the following Formulas 26 to 28), a fused ring compound group (forexample, the following Formulas 29 to 35), a fluorene-diyl group (forexample, the following Formulas 36 to 38), and a benzofluorene-diylgroup (for example, the following Formulas 39 to 46).

In Formulas 1 to 46, R has the same meaning as described above. In acase where there are a plurality of Rs, the plurality of Rs may be thesame or different from each other.

The constituent unit constituting the polymer compound, which is ap-type semiconductor material, may be a constituent unit in which two ormore types selected from the constituent unit represented by Formula(I), the constituent unit represented by Formula (II), and theconstituent unit represented by Formula (III) are combined and connectedto each other.

In a case where the polymer compound as a p-type semiconductor materialhas the constituent unit represented by Formula (I) and/or theconstituent unit represented by Formula (II), assuming that the amountof all the constituent units contained in the polymer compound is 100mol %, the total amount of the constituent unit represented by Formula(I) and the constituent unit represented by Formula (II) is usually 20to 100 mol %, and in order to improve charge transport properties as ap-type semiconductor material, it is preferably 40 to 100 mol %, andmore preferably 50 to 100 mol %.

Specific examples of the polymer compound as a p-type semiconductormaterial include polymer compounds represented by the following FormulasP-1 to P-6 (polymer compound P-1 to polymer compound P-6).

The coating liquid for forming an active layer may contain only one typeof p-type semiconductor material, or may contain two or more types inoptional ratio combination.

As a p-type semiconductor material, the polymer compound P-1 asdescribed above is preferably used from the viewpoint that a lightdetecting element having a narrow band sensitivity characteristic havinga narrow peak in the EQE spectrum with a small full width at halfmaximum (FWHM) can be realized particularly in the near infraredwavelength region.

(n-Type Semiconductor Material)

The n-type semiconductor material is preferably a fullerene derivative.The fullerene derivative means a compound in which at least a part offullerene (C60 fullerene, C70 fullerene, and C84 fullerene) is modified.

Examples of fullerene derivatives include compounds represented by thefollowing Formulas (N-1) to (N-4).

In Formulas (N-1) to (N-4), R^(a) represents an alkyl group, an arylgroup, a monovalent heterocyclic group, or a group having an esterstructure. A plurality of R^(a)s may be the same or different from eachother.

R^(b) represents an alkyl group or an aryl group. A plurality of R^(b)smay be the same or different from each other.

Examples of the group having an ester structure represented by R^(a)include a group represented by the following Formula (19).

In Formula (19), u1 represents an integer from 1 to 6. u2 represents aninteger from 0 to 6. R^(c) represents an alkyl group, an aryl group, ora monovalent heterocyclic group.

Examples of C₆₀ fullerene derivatives include the following compounds.

Specific suitable examples of the C₆₀ fullerene derivative include[6,6]-phenyl-C61 butyric acid methyl ester (C60PCBM, [6,6]-Phenyl-C61butyric acid methyl ester), and bisphenyl-C61 methyl butyrate (bisadductof phenyl C61-butyric acid methyl ester)

Specific examples of the C70 fullerene derivative include compoundsrepresented by the following formula.

Suitable specific examples of the C₇₀ fullerene derivative include[6,6]-phenyl-C71 butyric acid methyl ester (C70PCBM,[6,6]-phenyl-C71-butyric acid methyl ester), and inden C70 propionicacid hexyl ester (C70IPH, indene-C70-propionic acid hexyl ester).

As an n-type semiconductor material, C70PCBM, which is a C₇₀ fullerenederivative is preferably used from the viewpoint that a light detectingelement having a narrow band sensitivity characteristic having a narrowpeak in the EQE spectrum with a small full width at half maximum (FWHM)can be realized only in the near infrared wavelength region.

Specific examples of the C₈₄ fullerene derivative include [6,6]phenyl-C85 butyric acid methyl ester (C84PCBM, [6,6]-Phenyl C85 butyricacid methyl ester).

The coating liquid for forming an active layer may contain only one typeof n-type semiconductor material, or may contain two or more types inoptional ratio combination.

(Solvent)

The coating liquid for forming an active layer may contain only one typeof solvent, or may contain two or more types in optional ratiocombination. In a case where the coating liquid for forming an activelayer contains two or more kinds of solvents, the main solvent (referredto as a first solvent), which is the main component, and other additivesolvents (referred to as a second solvent) added to improve thesolubility are preferably contained. The first solvent and the secondsolvent will be described below.

(1) First Solvent

The solvent can be selected in consideration of the solubility in theselected p-type semiconductor material and the n-type semiconductormaterial, and the characteristics (boiling point, and the like) forcorresponding to the drying conditions when forming the active layer.

The first solvent as the main solvent is preferably aromatic hydrocarbon(hereinafter, simply referred to as an aromatic hydrocarbon) which mayhave a substituent (alkyl group or halogen atom). The first solvent ispreferably selected in consideration of the solubility of the selectedp-type semiconductor material and n-type semiconductor material.

Examples of such aromatic hydrocarbons include toluene, xylene (forexample, o-xylene, m-xylene, and p-xylene), trimethylbenzene (forexample, mesitylene, 1,2,4-trimethylbenzene (psoidoctene)), butylbenzene(for example, n-butylbenzene, sec-butylbenzene, and tert-butylbenzene),methylnaphthalene (for example, 1-methylnaphthalene), tetralin, indan,chlorobenzene, and dichlorobenzene (o-dichlorobenzene).

The first solvent may be formed of only one type of aromatic hydrocarbonor may be formed of two or more types of aromatic hydrocarbons. Thefirst solvent is preferably formed of only one aromatic hydrocarbon.

The first solvent is preferably one or more selected from the groupconsisting of toluene, o-xylene, m-xylene, p-xylene, mesitylene,pseudocumene, n-butylbenzene, sec-butylbenzene, tert-butylbenzene,methylnaphthalene, tetralin, indan, chlorobenzene, ando-dichlorobenzene, and more preferably o-xylene, pseudocumene,chlorobenzene, or o-dichlorobenzene.

(2) Second Solvent

The second solvent is preferably a solvent selected from the viewpointof facilitating the implementation of the producing step and furtherimproving the characteristics of the light detecting element. Examplesof the second solvent include a ketone solvent such as acetone, methylethyl ketone, cyclohexanone, acetophenone, and propiophenone, and anester solvent such as ethyl acetate, butyl acetate, phenyl acetate,ethyl cell solve acetate, methyl benzoate, butyl benzoate, and benzylbenzoate.

As the second solvent, acetophenone, propiophenone, or benzyl benzoateis preferable.

(3) Combination of First Solvent and Second Solvent

Suitable combinations of the first solvent and the second solventinclude, for example, a combination of o-xylene and acetophenone.

(4) Weight Ratio of First Solvent and Second Solvent

The weight ratio (first solvent:second solvent) of the first solvent,which is the main solvent, to the second solvent, which is theadditional solvent, is preferably in the range of 85:15 to 99:1 from theviewpoint of further improving the solubility of the p-typesemiconductor material and the n-type semiconductor material.

(5) Total Weight Percentage of First Solvent and Second Solvent

When the entire weight of the coating liquid is 100% by weight, thetotal weight of the first solvent and the second solvent contained inthe coating liquid is preferably 90% by weight or more, more preferably92% by weight or more, and further preferably 95% by weight or more fromthe viewpoint of further improving the solubility of the p-typesemiconductor material and the n-type semiconductor material, and it ispreferably 99% by weight or less, more preferably 98% by weight or less,and further preferably 97.5% by weight or less from the viewpoint ofincreasing the concentration of the p-type semiconductor material andthe n-type semiconductor material in the coating liquid so as tofacilitate the formation of a layer having a certain thickness or more.

(6) Other Optional Solvents

The solvent may contain any solvent other than the first solvent and thesecond solvent. When the total weight of all the solvents contained inthe coating liquid is 100% by weight, the content of other optionalsolvents is preferably 5% by weight or less, more preferably 3% byweight or less, and further preferably 1% by weight or less. As otheroptional solvents, solvents having a boiling point higher than that ofthe second solvent are preferable.

(Optional Components)

In addition to the first solvent, the second solvent, the p-typesemiconductor material, and the n-type semiconductor material, thecoating liquid may contain optional components such as an ultravioletabsorber, an antioxidant, a sensitizer for sensitizing the function ofgenerating electric charges by the generated light, and a lightstabilizer for increasing the stability from ultraviolet rays as long asthe object and effect of the present invention are not impaired.

(Concentration of p-Type Semiconductor Material and n-Type SemiconductorMaterial in Coating Liquid)

The total concentration of the p-type semiconductor material and then-type semiconductor material in the coating liquid is preferably 0.01%by weight or more and 20% by weight or less, more preferably 0.01% byweight or more and 10% by weight or less, further preferably 0.01% byweight or more and 5% by weight or less, and particularly preferably0.1% by weight or more and 5% by weight or less. The p-typesemiconductor material and the n-type semiconductor material may bedissolved or dispersed in the coating liquid. The p-type semiconductormaterial and the n-type semiconductor material are preferably at leastpartially dissolved, and more preferably all are dissolved.

(Preparation of Coating Liquid)

The coating liquid can be prepared by a known method. For example,coating liquid can be prepared by a method for mixing the first solventand the second solvent are mixed to prepare a mixed solvent and addingthe p-type semiconductor material and the n-type semiconductor materialto the mixed solvent, and a method for adding the p-type semiconductormaterial to the first solvent, adding the n-type semiconductor materialto the second solvent, and then mixing the first solvent and the secondsolvent to which each material has been added.

The first solvent, the second solvent, the p-type semiconductormaterial, and the n-type semiconductor material may be heated and mixedto a temperature equal to or lower than the boiling point of thesolvent.

After mixing the first solvent, the second solvent, the p-typesemiconductor material, and the n-type semiconductor material, theobtained mixture may be filtered using a filter, and the obtainedfiltrate may be used as a coating liquid. As the filter, for example, afilter formed of a fluororesin such as polytetrafluoroethylene (PTFE)can be used.

(Step of Forming Positive Electrode)

In this step, a positive electrode is formed on the active layer. In thepresent embodiment, the positive electrode is formed on the activelayer; however, in a case where the method for producing thephotoelectric conversion element includes a step of forming a holetransport layer which is an intermediate layer between the positiveelectrode and the active layer, the positive electrode is formed on thehole transport layer (hole injection layer).

The method for forming a positive electrode is not particularly limited.The positive electrode can be formed on the layer on which the positiveelectrode should be formed by forming the electrode material asdescribed above using a vacuum deposition method, a sputtering method,an ion plating method, a plating method, a coating method, or the like.

In a case where the material of the positive electrode is polyanilineand a derivative thereof, polythiophene and a derivative thereof,nanoparticles of the conductive substance, nanowire of the conductivesubstance, or nanotube of the conductive substance, a negative electrodecan be formed using an emulsion (emulsion), suspension (suspension), orthe like containing these materials and a solvent by a coating method.

In a case where the positive electrode is formed by the coating method,the positive electrode can be formed by using a coating liquidcontaining a conductive substance, a metal ink, a metal paste, a lowmelting point metal in a molten state, or the like. Examples of thecoating method of the coating liquid containing the material of thepositive electrode and the solvent include the same method as that inthe step of forming the active layer as described above.

Examples of the solvent contained in the coating liquid used whenforming the positive electrode by the coating method include ahydrocarbon solvent such as toluene, xylene, mesitylene, tetraline,decalin, bicyclohexyl, n-butylbenzene, sec-butylbezen, andtert-butylbenzene; a halogenized saturated hydrocarbon solvent such ascarbon tetrachloride, chloroform, dichloromethane, dichloroethane,chlorobutane, bromobutane, chloropentane, bromopentane, chlorohexane,bromohexane, chlorocyclohexane, and bromocyclohexane; a halogenatedunsaturated hydrocarbon solvent such as chlorobenzene, dichlorobenzene,and trichlorobenzene; an ether solvent such as tetrahydrofuran andtetrahydropyran; water; and alcohol. Specific examples of the alcoholinclude methanol, ethanol, isopropanol, butanol, ethylene glycol,propylene glycol, butoxyethanol, and methoxybutanol. The coating liquidmay contain one kind of solvent alone, may contain two or more kinds ofsolvents, and may contain two or more kinds of the above-describedsolvents.

(Step of Forming Hole Transport Layer)

The method for forming a hole transport layer in a case of forming thehole transport layer (hole injection layer) is not particularly limited.From the viewpoint of more simplifying the step of forming the holetransport layer, it is preferable to form the hole transport layer by acoating method. The hole transport layer can be formed, for example, byapplying a coating liquid containing the material and solvent of thehole transport layer as described above onto the active layer.

Examples of the solvent in the coating liquid used in the coating methodinclude water, alcohol, ketone, and hydrocarbon. Specific examples ofthe alcohol include methanol, ethanol, isopropanol, butanol, ethyleneglycol, propylene glycol, butoxyethanol, and methoxybutanol. Specificexamples of the ketone include acetone, methyl ethyl ketone, methylisobutyl ketone, 2-heptanone, and cyclohexanone. Specific examples ofthe hydrocarbons include n-pentane, cyclohexane, n-hexane, benzene,toluene, xylene, tetralin, chlorobenzene, and orthodichlorobenzene. Thecoating liquid may contain one kind of solvent alone, may contain two ormore kinds of solvents, and may contain two or more kinds of theabove-exemplified solvents. The amount of the solvent in the coatingliquid is preferably 1 part by weight or more and 10000 parts by weightor less, and more preferably 10 parts by weight or more and 1000 partsby weight or less with respect to 1 part by weight of the material ofthe hole transport layer.

Examples of the method (coating method) for applying the coating liquidcontaining the material of the hole transport layer and the solventinclude a spin coating method, a knife coating method, a casting method,a micro gravure coating method, a gravure coating method, and a barcoating method. Examples thereof include a roll coating method, a wirebar coating method, a dip coating method, a spray coating method, ascreen printing method, a flexographic printing method, an offsetprinting method, an ink jet printing method, a dispenser printingmethod, a nozzle coating method, and a capillary coating method. Amongthese, the spin coating method, the flexographic printing method, theink jet printing method, and the dispenser printing method arepreferable.

It is preferable to remove the solvent from the coating film bysubjecting the coating film obtained by applying the coating liquidcontaining the material of the hole transport layer and the solvent to aheat treatment, an air-drying treatment, a reduced pressure treatment,or the like.

(Step of Forming Positive Electrode)

In this embodiment, the positive electrode is usually formed on theactive layer. In a case where the method for producing the lightdetecting element according to the present embodiment includes a step offorming a hole transport layer, the positive electrode is formed on thehole transport layer.

The method for forming a positive electrode is not particularly limited.The positive electrode can be formed on the layer such as the activelayer and the hole transport layer, on which the positive electrodeshould be formed, by forming the material as described above using avacuum deposition method, a sputtering method, an ion plating method, aplating method, a coating method, or the like.

In a case where the material of the positive electrode is polyanilineand a derivative thereof, polythiophene and a derivative thereof,nanoparticles of the conductive substance, nanowire of the conductivesubstance, or nanotube of the conductive substance, the positiveelectrode can be formed using an emulsion (emulsion), suspension(suspension), or the like containing these materials and a solvent by acoating method.

In a case where the material of the positive electrode contains aconductive substance, the positive electrode can be formed by using acoating liquid containing a conductive substance, a metal ink, a metalpaste, a low melting point metal in a molten state, or the like.Examples of the coating method of the coating liquid containing thematerial of the positive electrode and the solvent include the samemethod as that in the step of forming the active layer as describedabove.

Examples of the solvent contained in the coating liquid used whenforming the positive electrode by the coating method include ahydrocarbon solvent such as toluene, xylene, mesitylene, tetraline,decalin, bicyclohexyl, n-butylbenzene, sec-butylbenzen, andtert-butylbenzene; a halogenized saturated hydrocarbon solvent such ascarbon tetrachloride, chloroform, dichloromethane, dichloroethane,chlorobutane, bromobutane, chloropentane, bromopentane, chlorohexane,bromohexane, chlorocyclohexane, and bromocyclohexane; a halogenatedaromatic hydrocarbon solvent such as chlorobenzene, dichlorobenzene, andtrichlorobenzene; an ether solvent such as tetrahydrofuran andtetrahydropyran; water; and alcohol. Specific examples of the alcoholinclude methanol, ethanol, isopropanol, butanol, ethylene glycol,propylene glycol, butoxyethanol, and methoxybutanol. The coating liquidmay contain one kind of solvent alone, may contain two or more kinds ofsolvents, and may contain two or more kinds of the above-describedsolvents.

EXAMPLES

Hereinafter, examples will be described in order to explain the presentinvention in more detail. The present invention is not limited to theexamples described below.

Example 1

(1) Producing of Light Detecting Element

A glass substrate having an ITO thin film (negative electrode) formedwith a thickness of 150 nm was prepared by a sputtering method, and asurface of the glass substrate was subjected to an ozone UV treatment.

Next, a solution obtained by diluting polyethyleneimine ethoxylate(PEIE) (available from Aldrich, trade name: polyethyleneimine, 80%ethoxylated solution, weight average molecular weight 110000), which isa modified product containing polyethyleneimine as a main chain andethylene oxide added to a nitrogen atom in the main chain 100 times withwater was used as a coating liquid, and the coating liquid was appliedby a spin coating method on a glass substrate on which a negativeelectrode was formed. The glass substrate coated with the coating liquidwas heated at 120° C. for 10 minutes using a hot plate to form theelectron transport layer 1 containing PEIE on the ITO thin film, whichis the negative electrode. The thickness of the electron transport layer1 was 1 nm. The work function of the electron transport layer 1 formedhere was measured (details will be described later).

Next, a polymer compound P-1 as a p-type semiconductor material andC60PCBM (available from Frontier Carbon Co., Ltd., trade name: E100,LUMO level: −4.3 eV) as an n-type semiconductor material were mixed at aweight ratio of 1/2 (p/n ratio), and the mixture was added to a mixedsolvent of o-xylene as the first solvent and acetophenone as the secondsolvent (o-xylene:acetophenone=95:5 (weight ratio)), and stirred at 80°C. for 10 hours to prepare a coating liquid for forming an active layer.

The prepared coating liquid for forming an active layer was applied ontothe electron transport layer of a glass substrate by the knife coatermethod, and the obtained coating film was dried for 5 minutes using ahot plate heated to 100° C. to form an active layer. The thickness ofthe formed active layer was 800 nm.

Next, in a resistance heating vapor deposition apparatus, molybdenumoxide (MoO₃) was deposited as a hole transport layer on the formedactive layer to a thickness of about 30 nm, and a silver (Ag) layer wasfurther formed as a positive electrode with a thickness of about 80 nm,thereby producing a light detecting element (photoelectric conversionelement).

Next, a UV curable sealant was applied on a glass substrate around theproduced light detecting element, the glass substrate which is thesealing substrate is bonded, and then UV light is emitted to seal thelight detecting element. The planar shape of the obtained lightdetecting element when viewed from the thickness direction was a squareof 2 mm×2 mm.

(2) Evaluation of Characteristics of Light Detecting Element

The external quantum efficiency (EQE) was measured using a spectralsensitivity measuring device (CEP-2000, available from Bunkoukeiki Co.,Ltd) with a bias voltage of −2 V applied to the produced light detectingelement. The full width at half maximum (FWHM) of the peak located onthe longest wavelength region of the EQE spectrum was calculated.Specifically, as for the full width at half maximum, when the value ofthe peak located on the longest wavelength region of the measured EQEspectrum peaks was set to 100% peak sensitivity, a peak width(wavelength width) corresponding to the peak sensitivity of 50% at thesame peak was calculated as the full width at half maximum. The resultsare indicated in Table 1.

As a result, such a peak was a narrow peak located in near infraredwavelength region with a full width at half maximum (FWHM) of 60 nm.That is, it was found that the light detecting element of Example 1 hasa narrow band sensitivity characteristic in the near infrared region.

(3) Evaluation of LUMO of n-Type Semiconductor Material Contained inActive Layer)

A LUMO level of the n-type semiconductor material was estimated fromcyclic voltammetry (CV) measurement values.

Specifically, LUMO of C60 PCBM, which is an n-type semiconductormaterial, was measured using a CV measuring device (ElectrochemicalAnalyzer Model 600B, available from BAS), by setting a dehydratedacetonitrile solution containing tetrabutylammonium hexafluorophosphate(TBAPF6, available from Aldrich) as a support electrolyte at aconcentration of 0.1 M, a film formed by dropping an n-typesemiconductor material dissolved in chloroform on platinum foil as awork electrode, platinum foil as a counter electrode, an Ag/AgClelectrode as a reference electrode, and a ferrocene potential as astandard potential. The LUMO of the obtained C60PCBM was −4.3 eV.

(4) Evaluation of Work Function (WF, eV) of Surface in Contact withActive Layer

As described above, the work function of the electron transport layer 1was evaluated using a Kelvin probe device using a glass substrate afterthe electron transport layer was formed as described above. As theKelvin probe device, FAC-2 available from RIKEN KEIKI Co., Ltd. wasused. Gold (WF: 5.1 eV) was used as a reference sample for calibration.The work function of the obtained electron transport layer was 4.2 eV.

Examples 2 and 3

A light detecting element was produced and EQE was measured in the samemanner as in Example 1 described above except that the thickness of theactive layer was set to 1000 nm (Example 2) and 1200 nm (Example 3). Thefull width at half maximum (FWHM) of the peak located on the longestwavelength side of the peaks of the EQE spectrum was calculated. Theresults are indicated in Table 1.

Comparative Example 1

A light detecting element was produced and EQE was measured in the samemanner as in Example 1 described above except that the thickness of theactive layer was set to 550 nm. The full width at half maximum (FWHM) ofthe peak located on the longest wavelength side of the peaks of the EQEspectrum was calculated. The results are indicated in Table 1.

Examples 4 and 5

A light detecting element was produced and EQE was measured in the samemanner as in Example 1 described above except that an electron transportlayer 2 having a thickness of 30 nm and containing zinc oxide was formedby using a zinc oxide dispersion liquid (available from TAYCACorporation, trade name: HTD-711Z), and the thickness of the activelayer was set to 1100 nm (Example 4) and 1400 nm (Example 5). The fullwidth at half maximum (FWHM) of the peak located on the longestwavelength side of the peaks of the EQE spectrum was calculated. Theresults are indicated in Table 1. The WF of electron transport layer 2was 4.2 eV.

Comparative Examples 2 and 3

A light detecting element was produced and EQE was measured in the samemanner as in Example 1 described above except that an electron transportlayer 2 having a thickness of 30 nm and containing zinc oxide was formedby using a zinc oxide dispersion liquid (available from TAYCACorporation, trade name: HTD-711Z), and the thickness of the activelayer was set to 650 nm (Comparative Example 2) and 750 nm (ComparativeExample 3). The full width at half maximum (FWHM) of the peak located onthe longest wavelength side of the peaks of the EQE spectrum wascalculated. The results are indicated in Table 1. The WF of electrontransport layer 2 was 4.2 eV.

Comparative Examples 4 to 12

A light detecting element was produced and EQE was measured in the samemanner as in Example 1 described above except that an electron transportlayer 3 having a thickness of 30 nm and containing zinc oxide was formedby using a zinc oxide dispersion liquid (available from Avantama, tradename: N-10), and the thickness of the active layer was set to 600 nm(Comparative Example 4), 800 nm (Comparative Example 5), 850 nm(Comparative Example 6), 950 nm (Comparative Example 7), 1100 nm(Comparative Example 8), 1400 nm (Comparative Example 9), 1800 nm(Comparative Example 10), 3000 nm (Comparative Example 11), and 3500 nm(Comparative Example 12). The full width at half maximum (FWHM) of thepeak located on the longest wavelength side of the peaks of the EQEspectrum was calculated. The results are indicated in Table 1. The WF ofelectron transport layer 3 was 4.4 eV.

Comparative Examples 13 to 16

A light detecting element was produced and EQE was measured in the samemanner as in Example 1 described above except that an electron transportlayer 4 having a thickness of 30 nm and containing titanium oxide wasformed by using a titanium (IV) isopropoxide solution (available fromAldrich), and the thickness of the active layer was set to 550 nm(Comparative Example 13), 1000 nm (Comparative Example 14), 1300 nm(Comparative Example 15), and 3200 nm (Comparative Example 16). The fullwidth at half maximum (FWHM) of the peak located on the longestwavelength side of the peaks of the EQE spectrum was calculated. Theresults are indicated in Table 1. The WF of electron transport layer 4was 4.7 eV.

Comparative Examples 17 to 20

A film having a thickness of 30 nm and containing zinc oxide was formedusing a solution of zinc oxide dispersion liquid (available from TAYCACorporation, trade name: HTD-711Z) diluted 10 times with 3-pentanol. Anelectron transport layer 5 was obtained by subjecting the formed film toa UV ozone treatment for 2 minutes. A light detecting element wasproduced and EQE was measured in the same manner as in Example 1described above except that the obtained electron transport layer 5 wasused, and the thickness of the active layer was set to 1000 nm(Comparative Example 17), 1200 nm (Comparative Example 18), 2000 nm(Comparative Example 19), and 3100 nm (Comparative Example 20). The fullwidth at half maximum (FWHM) of the peak located on the longestwavelength side of the peaks of the EQE spectrum was calculated.

The results are indicated in Table 1. The WF of electron transport layer5 was 4.6 eV.

Comparative Examples 21 and 22

A glass substrate on which an ITO thin film (negative electrode) wasformed was prepared, and the surface of this glass substrate wassubjected to an oxygen plasma treatment (150 W for 15 minutes), then asolution obtained by diluting polyethyleneimine ethoxylate (PEIE)(available from Aldrich, trade name polyethylene, 80% ethoxylatedsolution, weight average molecular weight 110000) 100 times with waterwas used to obtain an electron transport layer 6 having a thickness of10 nm and containing PEIE. A light detecting element was produced andEQE was measured in the same manner as in Example 1 described aboveexcept that the obtained electron transport layer 6 was used, and thethickness of the active layer was set to 600 nm (Comparative Example 21)and 1500 nm (Comparative Example 22). The full width at half maximum(FWHM) of the peak located on the longest wavelength side of the peaksof the EQE spectrum was calculated. The results are indicated inTable 1. The WF of electron transport layer 6 was 4.7 eV.

Examples 6 and 7

A photoelectric conversion element was prepared and measurement valuesof EQE were obtained in the same manner as in Example 1 described aboveexcept that C70IPH (available from Solenne, trade name: [C70]IPH, LUMOlevel: −4.3 eV) was used as the n-type semiconductor material containedin the active layer, the electron transport layer 1 described above wasused as the electron transport layer, and the thickness of the activelayer was set to 850 nm (Example 6) and 1100 nm (Example 7). The fullwidth at half maximum (FWHM) of the peak located on the longestwavelength side of the peaks of the EQE spectrum was calculated. Theresults are indicated in Table 2.

Comparative Example 23

A photoelectric conversion element was prepared and measurement valuesof EQE were obtained in the same manner as in Example 1 described aboveexcept that C70IPH (available from Solenne, trade name: [C70]IPH, LUMOlevel: −4.3 eV) was used as the n-type semiconductor material containedin the active layer, the electron transport layer 1 described above wasused as the electron transport layer, and the thickness of the activelayer was set to 500 nm. The full width at half maximum (FWHM) of thepeak located on the longest wavelength side of the peaks of the EQEspectrum was calculated. The results are indicated in Table 2.

Example 8

A light detecting element was prepared and measurement values of EQEwere obtained in the same manner as in Example 1 described above exceptthat C70IPH was used as the n-type semiconductor material contained inthe active layer, the electron transport layer 2 described above wasused as the electron transport layer, and the thickness of the activelayer was set to 1200 nm. The full width at half maximum (FWHM) of thepeak located on the longest wavelength side of the peaks of the EQEspectrum was calculated. The results are indicated in Table 2.

Comparative Examples 24 and 25

A light detecting element was prepared and measurement values of EQEwere obtained in the same manner as in Example 1 described above exceptthat C70IPH was used as the n-type semiconductor material contained inthe active layer, the electron transport layer 2 described above wasused as the electron transport layer, and the thickness of the activelayer was set to 250 nm (Comparative Example 24) and 750 nm (ComparativeExample 25). The full width at half maximum (FWHM) of the peak locatedon the longest wavelength side of the peaks of the EQE spectrum wascalculated. The results are indicated in Table 2.

Comparative Examples 26 and 27

A light detecting element was prepared and measurement values of EQEwere obtained in the same manner as in Example 1 described above exceptthat C70IPH was used as the n-type semiconductor material contained inthe active layer, the electron transport layer 3 was used as theelectron transport layer, and the thickness of the active layer was setto 800 nm (Comparative Example 26) and 1400 nm (Comparative Example 27).The full width at half maximum (FWHM) of the peak located on the longestwavelength side of the peaks of the EQE spectrum was calculated. Theresults are indicated in Table 2.

Comparative Examples 28 and 29

A photoelectric conversion element was produced and EQE was measured inthe same manner as in Example 1 described above except that C70IPH wasused as used as an n-type semiconductor material contained in the activelayer, an electron transport layer 7 having a thickness of 30 nm andcontaining zinc oxide was formed by using a zinc oxide dispersion liquid(available from Infinity PV, trade name Doped ZnO ink (water)), and thethickness of the active layer was set to 1000 nm (Comparative Example28) and 1500 nm (Comparative Example 29). The full width at half maximum(FWHM) of the peak located on the longest wavelength side of the peaksof the EQE spectrum was calculated. The results are indicated in Table2. In addition, the WF of electron transport layer 7 was 4.6 eV.

Example 9

A light detecting element was prepared and measurement values of EQEwere obtained in the same manner as in Example 1 except that C70PCBM(available from American Dye Source, trade name: ADS71BFA, LUMO level:−4.3 eV) was used as the n-type semiconductor material contained in theactive layer, the electron transport layer 1 described above was used asthe electron transport layer, and the thickness of the active layer wasset to 1300 nm. The full width at half maximum (FWHM) of the peaklocated on the longest wavelength side of the peaks of the EQE spectrumwas calculated. The results are indicated in Table 2.

Comparative Examples 30 and 31

A light detecting element was prepared and measurement values of EQEwere obtained in the same manner as in Example 1 except that C70PCBM(available from American Dye Source, trade name: ADS71BFA, LUMO level:−4.3 eV) was used as the n-type semiconductor material contained in theactive layer, the electron transport layer 1 described above was used asthe electron transport layer, and the thickness of the active layer wasset to 300 nm (Comparative Example 30) and 750 nm (Comparative Example31). The full width at half maximum (FWHM) of the peak located on thelongest wavelength side of the peaks of the EQE spectrum was calculated.The results are indicated in Table 2.

Examples 10 and 11

A light detecting element was prepared and measurement values of EQEwere obtained in the same manner as in Example 1 described above exceptthat C70PCBM was used as the n-type semiconductor material contained inthe active layer, the electron transport layer 2 described above wasused as the electron transport layer, and the thickness of the activelayer was set to 1500 nm (Example 10) and 2000 nm (Example 11). The fullwidth at half maximum (FWHM) of the peak on the longest wavelength sideof the peaks of the EQE spectrum was calculated. The results areindicated in Table 2.

Comparative Examples 32 and 33

A light detecting element was prepared and measurement values of EQEwere obtained in the same manner as in Example 1 described above exceptthat C70PCBM was used as the n-type semiconductor material contained inthe active layer, the electron transport layer 2 described above wasused as the electron transport layer, and the thickness of the activelayer was set to 250 nm (Comparative Example 32) and 650 nm (ComparativeExample 33). The full width at half maximum (FWHM) of the peak on thelongest wavelength side of the peaks of the EQE spectrum was calculated.The results are indicated in Table 2.

Comparative Examples 34 to 36

A light detecting element was prepared and measurement values of EQEwere obtained in the same manner as in Example 1 except that C70PCBM wasused as the n-type semiconductor contained in the active layer, theelectron transport layer 3 described above was used as the electrontransport layer, and the thickness of the active layer was set to 300 nm(Comparative Example 34), 800 nm (Comparative Example 35), and 1600 nm(Comparative Example 36). The full width at half maximum (FWHM) of thepeak located on the longest wavelength side of the peaks of the EQEspectrum was calculated. The results are indicated in Table 2.

Comparative Examples 37 to 39

A light detecting element was prepared and measurement values of EQEwere obtained in the same manner as in Example 1 described above exceptthat C70PCBM was used as the n-type semiconductor contained in theactive layer, the electron transport layer 7 described above was used asthe electron transport layer, and the thickness of the active layer wasset to 300 nm (Comparative Example 37), 900 nm (Comparative Example 38),and 1600 nm (Comparative Example 39). The full width at half maximum(FWHM) of the peak located on the longest wavelength side of the peaksof the EQE spectrum was calculated. The results are indicated in Table2.

Examples 12 to 14

A light detecting element was prepared and measurement values of EQEwere obtained in the same manner as in Example 1 except that a weightmixing ratio (p/n ratio) of the p-type semiconductor material to then-type semiconductor material contained in the active layer was set top/n=4/1 (Example 12), 10/1 (Example 13), 30/1 (Example 14), and thethickness of the active layer was set to 1500 nm. The full width at halfmaximum (FWHM) of the peak on the longest wavelength side of the peaksof the EQE spectrum was calculated. The results are indicated in Table3.

Comparative Example 40

A light detecting element was prepared and measurement values of EQEwere obtained in the same manner as in Example 1 except that a weightmixing ratio (p/n ratio) of the p-type semiconductor material to then-type semiconductor material contained in the active layer was set to100/1 and the thickness of the active layer was set to 1500 nm The fullwidth at half maximum (FWHM) of the peak on the longest wavelength sideof the peaks of the EQE spectrum was calculated. The results areindicated in Table 3.

TABLE 1 Differ- ence be- tween work Thick- n-type Elec- func- ness semi-tron Work tion of con- trans- func- and active ductor LUMO port tionLUMO layer FWHM material (eV) layer (eV) (eV) (nm) (nm) Compar- C60PCBM4.3 Elec- 4.2 −0.1 550 600 ative tron Example trans- 1 port Examplelayer 800 60 1 1 Example 1000 60 2 Example 1200 60 3 Compar- Elec- 4.2−0.1 650 600 ative tron Example trans- 2 port Compar- layer 750 600ative 2 Example 3 Example 1100 60 4 Example 1400 60 5 Compar- Elec- 4.40.1 600 600 ative tron Example trans- 4 port Compar- layer 800 600 ative3 Example 5 Compar- 850 600 ative Example 6 Compar- 950 600 ativeExample 7 Compar- 1100 600 ative Example 8 Compar- 1400 600 ativeExample 9 Compar- 1800 600 ative Example 10 Compar- 3000 600 ativeExample 11 Compar- 3500 600 ative Example 12 Compar- Elec- 4.7 0.4 550600 ative tron Example trans- 13 port Compar- layer 1000 600 ative 4Example 14 Compar- 1300 600 ative Example 15 Compar- 3200 600 ativeExample 16 Compar- Elec- 4.6 0.3 1000 600 ative tron Example trans- 17port Compar- layer 1200 600 ative 5 Example 18 Compar- 2000 600 ativeExample 19 Compar- 3100 600 ative Example 20 Compar- Elec- 4.7 0.4 600600 ative tron Example trans- 21 port Compar- layer 1500 600 ative 6Example 22

TABLE 2 Differ- ence be- tween work Thick- func- ness n-type Work tionof semi- Electron func- and active conductor LUMO transport tion LUMOlayer FWHM material (eV) layer (eV) (eV) (nm) (nm) Compar- C70IPH 4.3Electron 4.2 −0.1 500 600 ative transport Example layer 1 23 Example 85060 6 Example 1100 60 7 Compar- Electron 4.2 −0.1 250 600 ative transportExample layer 2 24 Compar- 750 600 ative Example 25 Example 1200 60 8Compar- Electron 4.4 0.1 800 600 ative layer 3 Example transport 26Compar- 1400 600 ative Example 27 Compar- Electron 4.6 0.3 1000 600ative layer 7 Example transport 28 Compar- 1500 600 ative Example 29Compar- C70PCBM 4.3 Electron 4.2 −0.1 300 600 ative transport Examplelayer 1 30 Compar- 750 600 ative Example 31 Example 1300 60 9 Compar-Electron 4.2 −0.1 250 600 ative transport Example layer 2 32 Compar- 650600 ative Example 33 Example 1500 60 10 Example 2000 60 11 Compar-Electron 4.4 0.1 300 600 ative transport Example layer 3 34 Compar- 800600 ative Example 35 Compar- 1600 600 ative Example 36 Compar- Electron4.6 0.3 300 600 ative transport Example layer 7 37 Compar- 900 600 ativeExample 38 Compar- 1600 600 ative Example 39

TABLE 3 Differ- ence between work n-type Work function semi- Electronfunc- and conductor LUMO transport tion LUMO p/n FWHM material (eV)layer (eV) (eV) ratio (nm) Example C60PCBM 4.3 Electron 4.2 −0.1 4/1 10012 transport Example layer 2 10/1 100 13 Example 30/1 100 14 Compar-100/1 ND ative Example 40

In Table 3, ND means that no peak was detected.

Hereinafter, the effects of the light detecting element according to thepresent embodiment will be described with reference to the drawings withreference to a part of examples and comparative examples.

FIGS. 4, 5, 6, and 7 illustrate the EQE spectrum (relative value) of thelight detecting element according to Example 3, Comparative Example 8,Comparative Example 21 and Example 7, respectively, and the absorptionspectrum (relative value) of the active layer according to Example 3,Comparative Example 8, Comparative Example 21, and Example 7,respectively.

As is clear from FIGS. 4 and 7 , in Examples 3 and 7, in a region ofwavelength 400 nm or more, the absorption peak located on the longestwavelength side is located near 810 nm, whereas among the peaks of theEQE spectrum, the peak located on the longest wavelength side is locatednear the wavelength of 870 nm, and is located in the near infraredwavelength region on the longer wavelength side.

On the other hand, the peak of the EQE spectrum did not appear near thewavelength of 810 nm where the absorption peak exists, and thesensitivity of EQE, that is, the light detecting element was lowered inthis wavelength region. As a result, in Examples 3 and 7, the full widthat half maximum (FWHM) of the peak of the EQE spectrum is a narrow peakof 60 nm in the near infrared wavelength region, and the light detectingelement according to the example has a specific high sensitivityparticularly in a narrow wavelength region in the near infraredwavelength region.

On the other hand, as illustrated in FIGS. 5 and 6 , the light detectingelement according to the comparative examples, in which the relationshipbetween the thickness of the active layer, the work function, and theLUMO energy level of the n-type semiconductor material does not meet therequirements as described above, had a broad sensitivity over a fairlywide range including the visible light wavelength region.

FIG. 8 illustrates the EQE spectrum (relative value) of the lightdetecting element according to Example 10 and the absorption spectrum(relative value) of the active layer. As is clear from FIG. 8 , ifC70PCBM is used as the n-type semiconductor material in the activelayer, the EQE in the visible light wavelength region can be suppressedto a low level. As a result, a narrow peak of the EQE spectrum with afull width at half maximum (FWHM) of 60 nm can be obtained only in thenear infrared wavelength region. That is, if C70PCBM is used, it ispossible to obtain a light detecting element having specifically highsensitivity only in a narrow wavelength region in the near infraredwavelength region.

FIGS. 9, 10, and 11 illustrate the EQE spectrum (relative value) of thelight detecting element according to Example 12, Example 13, and Example14 respectively, and the absorption spectrum (relative value) of theactive layer according to Example 12, Example 13, and Example 14,respectively.

As is clear from FIGS. 9, 10, and 11 , in Examples 3 and 7, in a regionof wavelength 400 nm or more, the absorption peak located on the longestwavelength side is located near 800 nm, whereas among the peaks of theEQE spectrum, the peak located on the longest wavelength side is locatednear the wavelength of 910 nm, and is located in the near infraredwavelength region on the longer wavelength side.

On the other hand, the peak of the EQE spectrum did not appear near thewavelength of 800 nm where the absorption peak exists, and thesensitivity of EQE, that is, the light detecting element was lowered inthis wavelength region. As a result, in Examples 12, 13, and 14, thefull width at half maximum (FWHM) of the peak of the EQE spectrum is anarrow peak of 100 nm in the near infrared wavelength region, and thelight detecting element according to the example has a specific highsensitivity particularly in a narrow wavelength region in the nearinfrared wavelength region.

As described above, by appropriately selecting and using various p-typesemiconductor materials and n-type semiconductor materials particularlyin consideration of the absorption wavelength thereof, the lightdetecting element having high sensitivity in a desired wavelength region(only) can be realized.

FIG. 12 illustrates the EQE spectrum (absolute value) of Examples 12 to14 and Comparative Example 40. As is clear from FIG. 12 , it isunderstood that there is a suitable ratio in the weight mixing ratio(p/n ratio) of the p-type semiconductor material to the n-typesemiconductor material in the active layer. That is, from Examples 12 to14, it is understood that the p/n ratio may be at least 4/1 to 30/1. Onthe other hand, it is understood that when the p/n ratio is 100/1, whichis more than 1/99, it does not function as a light detecting element andthus it is not possible to obtain the specific sensitivitycharacteristics in a predetermined wavelength region.

DESCRIPTION OF REFERENCE SIGNS

-   -   1 Image detector    -   2 Display device    -   10 Light detecting element    -   11, 210 Support substrate    -   12 Negative electrode    -   13 Electron transport layer    -   14 Active layer    -   15 Hole transport layer    -   16 Positive electrode    -   17, 240 Sealing substrate    -   20 CMOS transistor substrate    -   30 Interlayer insulating film    -   32 Interlayer wiring portion    -   40 Sealing layer    -   50 Color filter    -   100 Fingerprint detector    -   200 Display panel unit    -   200 a Display region    -   220 Organic EL element    -   230 Touch sensor panel

The invention claimed is:
 1. A light detecting element comprising: apositive electrode; a negative electrode; and an active layer providedbetween the positive electrode and the negative electrode and containinga p-type semiconductor material and an n-type semiconductor material,wherein a thickness of the active layer is at least 800 nm, a weightratio (p/n ratio) of the p-type semiconductor material to the n-typesemiconductor material contained in the active layer is at most 99/1,and a work function of a surface in contact with the active layer on thenegative electrode side is lower than an absolute value of a LUMO energylevel of the n-type semiconductor material.
 2. The light detectingelement according to claim 1, wherein external quantum efficiency has anarrow peak in a near infrared wavelength region.
 3. The light detectingelement according to claim 2, wherein a full width at half maximum ofthe narrow peak is at most less than 300 nm.
 4. The light detectingelement according to claim 1, wherein the surface is a surface of anelectron transport layer provided between the negative electrode and theactive layer.
 5. The light detecting element according to claim 1,wherein the n-type semiconductor material is a fullerene derivative. 6.The light detecting element according to claim 5, wherein the fullerenederivative is C70PCBM.
 7. The light detecting element according to claim2, wherein in a visible light wavelength region, the external quantumefficiency at the maximum absorption wavelength of the active layer isat most 20% of the maximum value of the external quantum efficiency ofthe narrow peak.
 8. An image sensor including the light detectingelement according to claim
 1. 9. The light detecting element accordingto claim 2, wherein the surface is a surface of an electron transportlayer provided between the negative electrode and the active layer. 10.The light detecting element according to claim 3, wherein the surface isa surface of an electron transport layer provided between the negativeelectrode and the active layer.
 11. The light detecting elementaccording to claim 2, wherein the n-type semiconductor material is afullerene derivative.
 12. The light detecting element according to claim3, wherein the n-type semiconductor material is a fullerene derivative.13. The light detecting element according to claim 4, wherein the n-typesemiconductor material is a fullerene derivative.
 14. The lightdetecting element according to claim 3, wherein in a visible lightwavelength region, the external quantum efficiency at the maximumabsorption wavelength of the active layer is at most 20% of the maximumvalue of the external quantum efficiency of the narrow peak.
 15. Thelight detecting element according to claim 4, wherein in a visible lightwavelength region, the external quantum efficiency at the maximumabsorption wavelength of the active layer is at most 20% of the maximumvalue of the external quantum efficiency of the narrow peak.
 16. Thelight detecting element according to claim 5, wherein in a visible lightwavelength region, the external quantum efficiency at the maximumabsorption wavelength of the active layer is at most 20% of the maximumvalue of the external quantum efficiency of the narrow peak.
 17. Thelight detecting element according to claim 6, wherein in a visible lightwavelength region, the external quantum efficiency at the maximumabsorption wavelength of the active layer is at most 20% of the maximumvalue of the external quantum efficiency of the narrow peak.
 18. Animage sensor including the light detecting element according to claim 2.19. An image sensor including the light detecting element according toclaim
 3. 20. An image sensor including the light detecting elementaccording to claim 4.